The Periodic Table & Trends

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Notes

The Periodic Table

Elements arranged in order of **increasing atomic number**.
Vertical columns are **groups** (numbered 1–7 and Group 0); horizontal rows are **periods** (numbered 1–7).
The **period number** equals the number of occupied electron shells.
The **group number** (for Groups 1–7) equals the number of outer shell electrons.
Group 0 elements have a full outer shell and are unreactive.
Metals are on the left, non-metals on the right, separated by a zig-zag line.

Electron Configuration & Position

Electronic configuration shows the number of electrons in each shell (e.g., carbon: 2,4).
The number of numbers in the configuration equals the **period number**.
The last number equals the **group number** (for Groups 1–7).
Example: chlorine (2,8,7) is in Period 3, Group 7.
Elements in the same group have the same number of outer electrons → similar chemical properties.

Metallic Character Trend

**Metallic character decreases** across a period (left to right).
**Metallic character increases** down a group.
Metals have 1–3 outer electrons; non-metals have 4–7 outer electrons.
Metals form **basic oxides**; non-metals form **acidic oxides**.
Metals are good conductors of electricity; non-metals are poor conductors.

Group 1 (Alkali Metals) Trends

Reactivity **increases** down the group (Li < Na < K < Rb < Cs < Fr).
Melting point **decreases** down the group.
They react with water to form a metal hydroxide and hydrogen gas.
Observations: Li fizzes slowly; Na moves rapidly; K burns with a lilac flame; Rb explodes; Cs violent explosion.

Group 7 (Halogens) Trends

Reactivity **decreases** down the group (F > Cl > Br > I).
Density **increases** down the group (F and Cl are gases, Br is liquid, I is solid at room temperature).
Halogens gain 1 electron to form ions with a 1– charge.
They are non-metals: poor conductors, brittle, low melting/boiling points.

Group 0 (Noble Gases)

All have a full outer shell of electrons (2 for He, 8 for others).
They are **unreactive** (inert) and exist as monatomic gases.
Used in lighting (neon signs) and as inert atmospheres (argon in welding).

Predicting Properties

Trends down groups and across periods allow prediction of **melting point, boiling point, density, and reactivity**.
Transition elements are denser than Group 1 elements.
Given data for a group, arrange elements in order of position to identify trends.
Francium is too reactive and rare to confirm predictions experimentally.

Bohr model of sodium atom showing electron shells (2,8,1) – Period 3, Group 1.

Bohr model of chlorine atom showing electron shells (2,8,7) – Period 3, Group 7.

Practice questions

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1.Which one of the following names does not correspond to a group of elements on the Periodic table?
Easy
- AAlkali
- BGroup VI
- CAlloys
- DHalogens
2.Which row describes how the elements are positioned on the Periodic table and the names used?
Easy
- Aelements placed by atomic number; group = vertical column; period = horizontal row
- Belements placed by mass number; group = vertical column; period = horizontal row
- Celements placed by atomic number; group = horizontal row; period = vertical column
- Delements placed by mass number; group = horizontal row; period = vertical column
3.Which property of elements increases as you move across the Periodic table?
Easy
- AThe number of outer shells increases.
- BThe number of outer shell electrons increases.
- CThe metallic character.
- DThe tendency to become oxidised.
4.Element Z forms an ion with a 2- charge. Which group of the Periodic Table is element Z found in?
Easy
- A1
- B2
- C6
- D7
5.Element X is found in Group 7 of the Periodic Table. Which properties are typical of element X? 1. Poor conductor of electricity 2. Malleable 3. High melting points 4. Form acidic oxides
Easy
- A1 and 2
- B1 and 4
- C2 and 3
- D3 and 4
6.The table shows the densities at room temperature of halogens W, X, Y and Z: W 0.0017 g/cm3, X 3.1 g/cm3, Y 0.0032 g/cm3, Z 4.93 g/cm3. Which row correctly identifies W, X, Y and Z?
Medium
- AW=fluorine, X=chlorine, Y=bromine, Z=iodine
- BW=fluorine, X=bromine, Y=chlorine, Z=iodine
- CW=iodine, X=chlorine, Y=bromine, Z=fluorine
- DW=iodine, X=bromine, Y=chlorine, Z=fluorine
7.Potassium and krypton are elements in Period 4. Potassium is at the beginning of the period and is more metallic than krypton which is at the end of the period. What makes potassium more metallic than krypton?
Medium
- AIt has less electrons than krypton.
- BIt has less protons than krypton.
- CIt has less electron shells.
- DIt has less outer shell electrons.
8.The elements of the Periodic table can be broadly classified into metals and nonmetals. Which statements are correct? 1. Magnesium is more metallic than silicon. 2. Boron is more metallic than lithium. 3. Carbon is less metallic than beryllium. 4. Sodium is less metallic than aluminium.
Medium
- A1 and 3
- B1 and 2
- C2, 3 and 4
- D1, 2 and 4

Slides

The Periodic Table

Elements are arranged in order of increasing atomic number.
Vertical columns are called groups; horizontal rows are called periods.
Group number shows number of outer electrons; period number shows number of electron shells.

Which row correctly describes how elements are positioned on the Periodic Table?

Atomic number, vertical column, horizontal row
Mass number, vertical column, horizontal row
Atomic number, horizontal row, vertical column
Mass number, horizontal row, vertical column

Groups and Periods

Periods are numbered 1–7; elements in Period 2 have 2 electron shells.
Groups are numbered 1–7 and Group 0; Group 1 elements have 1 outer electron.
Group number helps predict ion charge: metals lose electrons (e.g., Group 1 → +1), non-metals gain electrons (e.g., Group 7 → -1).

An element with electronic configuration 2,8,6 is in Group ____ and Period ____.

Metallic Character Trend

Metallic character decreases across a period (left to right).
Metallic character increases down a group.
Metals are on the left, non-metals on the right; metalloids lie between.

Which of these are true about metals and non-metals?

Metals are good conductors of electricity.
Non-metals form basic oxides.
Metals are malleable and have high melting points.
Non-metals have 1–3 outer shell electrons.

Electronic Configuration and Position

Electronic configuration shows number of occupied shells (period) and outer electrons (group).
Example: Chlorine (2,8,7) is in Period 3, Group 7.
Elements in the same group have similar chemical properties because they have the same number of outer electrons.

An element has electronic configuration 2,8,2. Which group and period is it in?

Group 2, Period 3
Group 3, Period 2
Group 2, Period 2
Group 8, Period 2

Trends Down a Group

Down Group 1: reactivity increases, melting point decreases.
Down Group 7: reactivity decreases, melting and boiling points increase.
Down a group, atoms have more electron shells, so outer electrons are further from nucleus.

Going down Group 7, the number of electron shells ____ so the outer electron is ____ the nucleus, making it harder to ____ an electron.

Predicting Properties

Trends allow prediction of properties like boiling point, density, and reactivity.
Example: Group 1 reactivity increases down the group (Li < Na < K).
Francium is predicted to be extremely reactive, but it is rare and radioactive.

Which statement explains why potassium is more reactive than lithium?

Potassium has more electron shells, so its outer electron is lost more easily.
Potassium has fewer electron shells, so its outer electron is held more tightly.
Potassium has more protons, so it attracts electrons more strongly.
Potassium has a higher melting point, so it reacts faster.

Metallic Character and Electron Loss

Metals tend to lose electrons; non-metals tend to gain electrons.
Across a period, atoms have more outer electrons and are closer to a full shell, so they gain electrons more readily (less metallic).
Down a group, atoms lose electrons more easily (more metallic).

Which statements about metallic character are correct?

Magnesium is more metallic than silicon.
Boron is more metallic than lithium.
Carbon is less metallic than beryllium.
Sodium is less metallic than aluminium.

Properties of Halogens

Halogens (Group 7) are non-metals: poor conductors, brittle, low melting points (increase down group).
They form acidic oxides and diatomic molecules (e.g., Cl2).
Density increases down the group (fluorine gas → iodine solid).

Which properties are typical of a Group 7 element?

Poor conductor of electricity and forms acidic oxides
Malleable and high melting point
Good conductor of electricity and forms basic oxides
Brittle and forms basic oxides

Identifying Trends from Data

Given data for elements in a group, arrange them in order of position to see trends.
Example: Density of halogens increases down the group (F < Cl < Br < I).
Reactivity of Group 1 with water increases down the group (Li fizzes, Na more vigorous, K burns).

The density of halogens at room temperature increases down the group. Fluorine is a gas, chlorine is a gas, bromine is a ____, iodine is a ____.

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