The Periodic Table: Classification Of Elements

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The Periodic Table: Structure and Organisation

The Periodic Table lists all known elements in order of increasing atomic number (1 to 118).
Elements are arranged so that atoms with the same number of electron shells are in the same period (row).
Elements with similar outer-shell electron configurations are placed in the same group (column).
Period number equals the number of occupied electron shells; group number indicates the number of valence electrons.
Hydrogen is placed in its own group because its properties do not closely match any single group.
Helium is in Group 18 because it shares the unreactive nature of noble gases, despite having only 2 electrons.

The Periodic Table

Metals, Non-Metals and Metalloids

Metals are found on the left and centre of the table (s- and d-blocks, and part of the p-block). They are good conductors of heat and electricity, and are malleable/ductile.
Non-metals are on the right-hand side (p-block). They are poor conductors, brittle when solid, and often form acidic oxides.
Metalloids lie along a diagonal boundary between metals and non-metals and show properties of both.
Examples of metalloids include boron, silicon, arsenic and antimony.

Metals and non-metals in the Periodic Table

Blocks of the Periodic Table

Elements are classified into four blocks based on their electron configuration: s, p, d, f.
s-block: Groups 1 and 2 plus helium; outer electrons are in s orbitals.
p-block: Groups 13 to 18; outer electrons are in p orbitals.
d-block: Transition metals (Groups 3 to 12); outer electrons are in d orbitals.
f-block: Lanthanides and actinides; outer electrons are in f orbitals.
Block position helps predict reactivity, oxidation states and bonding behaviour.

Electron Configurations and the Periodic Table

Electron configuration shows how electrons are arranged in shells, sub-shells and orbitals.
The period number indicates the highest occupied principal energy level (shell).
The group number indicates the number of valence electrons.
The block is determined by the type of orbital (s, p, d, f) occupied by the outermost electrons.
In the p-block, the element's position from left to right gives the number of electrons in the p subshell.
The 4s orbital is lower in energy than the 3d subshell, so it is filled first (e.g. potassium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹).
Shorthand notation uses the nearest preceding noble gas in brackets, e.g. potassium is [Ar] 4s¹.

Electron shells and the Periodic Table

Periodic Trends: Atomic and Ionic Radius

Atomic radius is the distance from the nucleus to the outermost electron shell.
Across a period, atomic radius generally decreases because nuclear charge increases while shielding remains roughly constant, pulling electrons closer.
Down a group, atomic radius generally increases because more principal quantum shells are added, increasing distance and shielding.
Cations are smaller than their parent atoms due to loss of an outer shell and reduced electron–electron repulsion.
Anions are larger than their parent atoms because extra electrons increase repulsion, spreading the electron cloud.
Ionic radius decreases across a period for cations, then increases sharply when anions form, then decreases again.
Ionic radius increases down a group as more electron shells are added.

Periodic Trends: Ionisation Energy

First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Ionisation energies are measured under standard conditions (298 K and 100 kPa) and have units kJ mol⁻¹.
Across a period, ionisation energy generally increases because nuclear charge increases while shielding stays roughly constant, so outer electrons are held more strongly.
Down a group, ionisation energy generally decreases because outer electrons are further from the nucleus and experience more shielding.
There is a rapid decrease in ionisation energy between the end of one period and the start of the next due to increased distance and shielding.
Example: Ca(g) → Ca⁺(g) + e⁻, ΔH = +590 kJ mol⁻¹.

Periodic Trends: Electron Affinity and Electronegativity

Electron affinity is the energy released when one mole of electrons is gained by one mole of gaseous atoms to form one mole of gaseous ions.
First electron affinity is usually exothermic for non-metals (e.g. Cl(g) + e⁻ → Cl⁻(g), ΔH = –349 kJ mol⁻¹).
Some elements (Group 2, Group 12, Group 15) have positive (endothermic) first electron affinities due to stable or half-filled subshells.
Second electron affinity is endothermic because energy is needed to overcome repulsion between an electron and a negative ion.
Electron affinity becomes more negative (more exothermic) across a period and less negative down a group.
Electronegativity is the ability of an atom to attract a pair of electrons towards itself in a covalent bond.
Electronegativity increases across a period and decreases down a group.
Electronegativity differs from electron affinity: it applies only to covalent bonding, while electron affinity is a measurable thermodynamic value for forming negative ions.

Group 1 Metals with Water

Group 1 metals are called alkali metals because they form alkaline solutions with high pH when reacted with water.
They are soft, shiny when freshly cut, good conductors, with low melting points and low densities.
They react vigorously with water to form an alkaline metal hydroxide solution and hydrogen gas: 2M(s) + 2H₂O(l) → 2MOH(aq) + H₂(g).
Lithium floats and reacts slowly; sodium reacts more vigorously, melting into a silvery ball; potassium reacts violently, igniting hydrogen with a lilac flame.
Reactivity increases down Group 1 because the outer electron is further from the nucleus and more shielded, so it is more easily lost.
Alkali metals react vigorously with halogens to form alkali metal halides, e.g. 2Na(s) + Cl₂(g) → 2NaCl(s).

Group 17 Elements with Halide Ions

The halogens are Group 17 non-metals: fluorine, chlorine, bromine, iodine and astatine.
They are diatomic and have seven electrons in their outer shell, forming halide ions by gaining one electron.
Colours and states at room temperature: fluorine (yellow gas), chlorine (pale green gas), bromine (orange-brown liquid), iodine (grey-black solid).
Melting and boiling points increase down the group due to increasing molecular mass and stronger van der Waals forces.
Reactivity decreases down Group 17 because atomic radius and shielding increase, making it harder to attract an incoming electron.
A more reactive halogen will displace a less reactive halogen from an aqueous solution of its halide: Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq).
Reactivity order: chlorine > bromine > iodine.

Metallic and Non-Metallic Oxides

Across a period, oxides change from basic through amphoteric to acidic.
Basic oxides (e.g. Na₂O, MgO) are ionic solids that form alkaline hydroxides in water: Na₂O(s) + H₂O(l) → 2NaOH(aq).
Amphoteric oxides (e.g. Al₂O₃) can react with both acids and bases.
Acidic oxides (e.g. SiO₂, P₄O₁₀, SO₂, SO₃) are covalent and form acids in water: SO₂(g) + H₂O(l) → H₂SO₃(aq).
The trend from basic to acidic is explained by decreasing electronegativity difference between the element and oxygen across the period.
Non-metal oxides dissolving in atmospheric water cause acid rain; CO₂ dissolving in seawater causes ocean acidification.

Metals form basic oxides, non-metals form acidic oxides

Oxidation States

Oxidation can be defined as addition of oxygen, loss of hydrogen, or loss of electrons.
Reduction can be defined as loss of oxygen, gain of hydrogen, or gain of electrons.
The oxidation number of an atom is the charge it would have if all bonding were completely ionic.
Rules: uncombined elements = 0; Group 1 = +1; Group 2 = +2; fluorine = –1; hydrogen = +1 (or –1 in metal hydrides); oxygen = –2 (except peroxides = –1, F₂O = +2).
The sum of oxidation numbers in a neutral compound is 0; in a polyatomic ion it equals the ion's charge.
In compounds/ions, the more electronegative element gets the negative oxidation number.
Oxidation numbers can be fractional when averaged across atoms in different environments (e.g. S in S₄O₆²⁻ is +2.5).
Stock notation uses Roman numerals for variable oxidation states, e.g. iron(II) oxide (FeO) and iron(III) oxide (Fe₂O₃).

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Übungsfragen

Gratis-Vorschau — 8 von 63 Fragen. Registriere dich, um alle zu sehen.

1.State the property that determines the order in which elements are arranged in the periodic table.
Medium
- AAtomic number
- BAtomic mass
- CNumber of neutrons
- DElectron affinity
2.State the relationship between the electron arrangement of an element and its group and period in the periodic table.
Medium
- AGroup number equals the number of occupied electron shells; period number equals the number of valence electrons.
- BGroup number equals the number of valence electrons; period number equals the number of occupied electron shells.
- CGroup number equals the number of protons; period number equals the number of neutrons.
- DGroup number equals the number of valence electrons; period number equals the number of valence electrons.
3.The elements in the periodic table are arranged in order of increasing atomic mass.
Easy
True or false?
4.Which block of the periodic table contains elements whose outer electrons are in p orbitals?
Medium
- As-block
- Bp-block
- Cd-block
- Df-block
5.Which of the following statements about the periodic table are correct? (select all that apply)
Medium
- AHydrogen is placed in its own group because its properties do not match any one group closely.
- BHelium is placed in Group 18 because it shares the unreactive nature of the noble gases.
- CMetalloids are found along a diagonal boundary between metals and non-metals.
- DAll non-metals are found in the s-block.
- EGroup 1 elements are known as the halogens.
6.Match each group with its correct name.
Medium
- Group 1
- Group 17
- Group 18
- Groups 3–12
- Alkali metals
- Halogens
- Noble gases
- Transition elements
7.An element has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁵. In which group and period is it found?
Medium
- AGroup 17, Period 3
- BGroup 7, Period 3
- CGroup 15, Period 3
- DGroup 17, Period 2
8.Which of the following are properties of metals? (select all that apply)
Medium
- AGood conductors of heat and electricity
- BMalleable and ductile
- CBrittle when solid
- DOften form acidic oxides
- EFound on the left and centre of the periodic table

Mehr Fragen

9.Match each block of the periodic table with the type of orbital that contains its outer electrons.
Easy
- s-block
- p-block
- d-block
- f-block
- f orbitals
- s orbitals
- d orbitals
- p orbitals
10.Which of the following statements about metalloids are correct? (select all that apply)
Medium
- AThey are found along a diagonal boundary between metals and non-metals.
- BThey exhibit properties of both metals and non-metals.
- CBoron, silicon, arsenic and antimony are examples.
- DThey are all found on the left-hand side of the periodic table.
- EThey are all good conductors of electricity like copper.
11.Place these Period 3 oxides in order of increasing pH of the solution formed when each is added to water, from lowest pH to highest pH.
Medium
- P4O10
- Al2O3 (amphoteric, no reaction with water)
- MgO
- Na2O
12.Which statement correctly describes the change in the acid-base character of the Period 3 oxides from Na2O to Cl2O7?
Medium
- ABasic → amphoteric → acidic
- BAcidic → amphoteric → basic
- CBasic → acidic → amphoteric
- DAmphoteric → basic → acidic
13.Metallic oxides tend to form hydroxides in water, giving alkaline solutions.
Easy
True or false?
14.Which oxide produces the solution with the highest pH when added to water?
Medium
- ACO2
- BSO3
- CCaO
- DNa2O
15.There is an increase in boiling point moving from HCl to HI. Which statement best explains this trend?
Medium
- AThe molecules become more polar down the group.
- BThe number of electrons increases, so van der Waals forces between molecules become stronger.
- CHydrogen bonding becomes stronger down the group.
- DThe molecules become smaller, so they pack more closely.
16.Which of the following statements about halogen displacement reactions are correct? (select all that apply)
Medium
- APotassium chloride solution will react with fluorine to form chlorine.
- BSodium chloride solution will react with iodine to form chlorine.
- CLithium iodide solution will react with bromine to form iodine.
- DA more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.
- EReactivity of the halogens increases down Group 17.
17.Match each halogen with its colour and state at room temperature.
Medium
- Fluorine
- Chlorine
- Bromine
- Iodine
- Grey-black solid that sublimes to a purple vapour
- Pale green gas
- Yellow gas
- Orange-brown liquid that evaporates to a brown gas
18.Which pair of elements has the most vigorous reaction?
Medium
- ACs and I
- BLi and Cl
- CCs and F
- DLi and F
19.What would the student expect to observe with the litmus paper?
Medium
- APotassium oxide turns red litmus blue; selenium oxide turns blue litmus red.
- BBoth solutions turn blue litmus red.
- CBoth solutions turn red litmus blue.
- DPotassium oxide turns blue litmus red; selenium oxide turns red litmus blue.
20.Which of the four oxides would conduct electricity in their molten state?
Medium
- AAll four oxides
- BOnly the acidic oxides
- COnly the basic and amphoteric oxides
- DNone of the oxides
21.For the solutions formed by dissolving the oxides in water, which are correctly classified? (select all that apply)
Medium
- APotassium oxide solution is alkaline.
- BSelenium oxide solution is acidic.
- CMagnesium oxide solution is acidic.
- DSulfur trioxide solution is alkaline.
22.An element has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴. Which block of the periodic table does this element belong to?
Medium
- As-block
- Bp-block
- Cd-block
- Df-block
23.An element X is in Period 4 and Group 6. Which statement about X is correct?
Medium
- AX has 4 valence electrons.
- BX is a transition element.
- CX has 6 occupied energy levels.
- DX forms an ion with a 2– charge.
24.Which of the following statements about the element with electron configuration [Ar] 4s² 3d¹⁰ 4p³ are correct? (select all that apply)
Medium
- AIt is in the p-block.
- BIt is in Group 15.
- CIt has 3 valence electrons.
- DIt is in Period 4.
- EIt is a transition element.
25.A cation is always larger than its parent atom because it has a higher nuclear charge.
Easy
True or false?
26.Match each element with its correct block in the periodic table.
Medium
- Calcium
- Chlorine
- Iron
- Uranium
- s-block
- p-block
- d-block
- f-block
27.Place the following elements in order of increasing atomic radius (smallest to largest).
Medium
- Fluorine
- Lithium
- Potassium
- Sodium
28.The graph of first ionisation energy against atomic number for Period 2 shows a general increase from lithium to neon, but there is a drop from beryllium to boron and from nitrogen to oxygen. Which statement best explains the drop from beryllium to boron?
Medium
- ABoron has a larger atomic radius than beryllium.
- BThe electron removed from boron is in a 2p orbital, which is higher in energy than the 2s orbital it is removed from in beryllium.
- CBoron has more shielding than beryllium.
- DBoron has a lower nuclear charge than beryllium.
29.A student adds a small piece of sodium to a trough of water and collects the gas produced in a test tube. They then hold a lit splint to the mouth of the test tube. What is the correct observation and conclusion?
Medium
- AA squeaky pop is heard; the gas is hydrogen
- BThe splint relights; the gas is oxygen
- CA white precipitate forms; the gas is carbon dioxide
- DThe lit splint is extinguished; the gas is hydrogen
30.A student adds chlorine solution to colourless potassium bromide solution in a test tube. What colour change would be observed, and why?
Medium
- AColourless to orange, because chlorine is more reactive and displaces bromine
- BColourless to brown, because bromine displaces chlorine
- CPale green to colourless, because chlorine is reduced
- DColourless to purple, because iodine is formed
31.A sample of an oxide is added to water and the resulting solution is tested with universal indicator paper, which turns blue. The oxide is most likely to be:
Medium
- ASodium oxide
- BSulfur dioxide
- CPhosphorus pentoxide
- DCarbon dioxide
32.A student adds a piece of freshly cut potassium to cold water. Which set of observations is correct?
Medium
- AThe potassium melts into a shiny ball that dashes around, hydrogen is released rapidly, and a lilac flame may be seen
- BThe potassium sinks and fizzes slowly, producing a popping sound
- CThe potassium reacts to form a white precipitate of potassium hydroxide
- DThe potassium does not react because it is less reactive than lithium
33.A student adds dilute hydrochloric acid to a sample of an unknown oxide. The oxide dissolves to form a colourless solution. When the same oxide is added to sodium hydroxide solution, it also dissolves. The oxide is:
Hard
- AAluminium oxide
- BSodium oxide
- CSilicon dioxide
- DSulfur dioxide
34.A student is investigating the trend in reactivity of Group 1 metals with water. They have samples of lithium, sodium and potassium. Which statement about the expected observations is correct?
Medium
- APotassium reacts most vigorously, followed by sodium, then lithium
- BLithium reacts most vigorously because it is smallest
- CAll three react at the same rate because they are in the same group
- DSodium reacts most vigorously because it is in the middle of the group
35.A student adds a small piece of calcium to water and tests the resulting solution with red litmus paper. Which of the following observations are correct? (select all that apply)
Medium
- ABubbles of gas are produced
- BThe calcium sinks and reacts steadily
- CThe red litmus paper turns blue
- DThe solution formed is acidic
- EA white precipitate of calcium hydroxide may form if the solution is concentrated
36.A student sets up a displacement reaction by adding bromine water to a solution of potassium iodide. Which statements about this reaction are correct? (select all that apply)
Hard
- AThe solution turns brown
- BBromine is more reactive than iodine
- CIodine is displaced from the iodide ions
- DThe reaction produces potassium bromide
- EBromine is oxidised in this reaction
37.A more reactive halogen will displace a less reactive halogen from an aqueous solution of its halide.
Easy
True or false?
38.When sodium oxide is added to water, the resulting solution has a pH of about 14.
Easy
True or false?
39.The first electron affinity of iodine is more exothermic than that of bromine.
Medium
True or false?
40.Match each halogen with its correct colour and state at room temperature.
Medium
- Fluorine
- Chlorine
- Bromine
- Iodine
- Yellow gas
- Pale green gas
- Orange-brown liquid
- Grey-black solid
41.Complete the sentence about the blocks of the periodic table.
Easy
The s-block contains Groups 1 and 2 plus helium; the p-block contains Groups 13 to 18; the d-block contains transition metals; the f-block contains lanthanides and actinides. Elements in the s-block have outer electrons in ____ orbitals, while elements in the p-block have outer electrons in ____ orbitals.
42.How many valence electrons does an element in Group 2 have?
Medium
43.Using the electronegativity values Na = 0.9, Mg = 1.2, Al = 1.5, Si = 1.8, P = 2.1, S = 2.5, and O = 3.4, calculate the electronegativity difference (ΔEN) for the bond between oxygen and aluminium in Al₂O₃.
Medium
44.Complete the following sentences about periodic trends.
Medium
Across a period, atomic radius generally ____. Down a group, atomic radius generally ____.
45.What is the name of the element in Period 3 and Group 14?
Medium
46.How many electrons are in the outermost shell of an element in Group 2?
Medium
47.Using the electronegativity values Na = 0.9, Mg = 1.2, Al = 1.5, Si = 1.8, P = 2.1, S = 2.5, and O = 3.4, calculate the electronegativity difference (ΔEN) for the bond between sulfur and oxygen in SO2. Give your answer to one decimal place.
Medium
48.How many electrons are in the 3d subshell of an Fe³⁺ ion? (Atomic number of Fe = 26)
Medium
49.Complete the sentence about ionisation energy.
Medium
The first ionisation energy is the energy required to remove one mole of electrons from one mole of ____ atoms to form one mole of ____ ions.
50.Using the electronegativity values Na = 0.9, Mg = 1.2, Al = 1.5, Si = 1.8, P = 2.1, S = 2.5, and O = 3.4, calculate the electronegativity difference (ΔEN) for the bond between magnesium and oxygen in MgO. Give your answer to one decimal place.
Medium
51.What is the general trend in atomic radius down a group?
Easy
52.Complete the sentence about Group 1 reactivity.
Medium
The reactivity of Group 1 metals ____ down the group because the outermost electron is ____ from the nucleus.
53.Define the term first ionisation energy and state what is meant by the term periodicity.
Medium
54.Distinguish between the terms group and period.
Easy
55.Explain why the first ionisation energy of potassium is smaller than that of calcium.
Medium
56.Explain why the boiling point of HF is much higher than the boiling point of the other hydrogen halides.
Hard
57.Explain why the atomic radius decreases across Period 3 from sodium to chlorine.
Hard
58.How many valence electrons does an element in Group 2 have?
Medium
- A3
- B4
- C2
- D1
59.Using the electronegativity values Na = 0.9, Mg = 1.2, Al = 1.5, Si = 1.8, P = 2.1, S = 2.5, and O = 3.4, calculate the electronegativity difference (ΔEN) for the bond between oxygen and aluminium in Al₂O₃.
Medium
- A2.9
- B0.9
- C1.9
- D3.9
60.How many electrons are in the outermost shell of an element in Group 2?
Medium
- A1
- B2
- C3
- D4
61.Using the electronegativity values Na = 0.9, Mg = 1.2, Al = 1.5, Si = 1.8, P = 2.1, S = 2.5, and O = 3.4, calculate the electronegativity difference (ΔEN) for the bond between sulfur and oxygen in SO2. Give your answer to one decimal place.
Medium
- A2.9
- B1.9
- C-0.1
- D0.9
62.How many electrons are in the 3d subshell of an Fe³⁺ ion? (Atomic number of Fe = 26)
Medium
- A4
- B5
- C6
- D7
63.Using the electronegativity values Na = 0.9, Mg = 1.2, Al = 1.5, Si = 1.8, P = 2.1, S = 2.5, and O = 3.4, calculate the electronegativity difference (ΔEN) for the bond between magnesium and oxygen in MgO. Give your answer to one decimal place.
Medium
- A1.2
- B2.2
- C3.2
- D4.2

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