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Atomic Structure And The Periodic Table

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课程笔记

Elements, Compounds & Mixtures

  • An element is a substance made of atoms with the same number of protons; it cannot be split chemically.
  • A compound is a pure substance of two or more elements chemically combined; it cannot be separated by physical means.
  • A mixture is a combination of substances not chemically combined; it can be separated by physical methods like filtration or evaporation.
  • Examples: element – oxygen; compound – carbon dioxide (CO₂); mixture – sand and water.

Particle diagram showing elements, compounds and mixtures

Particle diagram showing elements, compounds and mixtures

Atomic Structure

  • Atoms consist of a nucleus (protons + neutrons) surrounded by electrons in shells.
  • Protons have relative mass 1 and charge +1; neutrons have mass 1 and charge 0; electrons have negligible mass and charge –1.
  • The atomic number (Z) is the number of protons; it defines the element.
  • The mass number (A) is the total number of protons + neutrons.
  • Number of neutrons = mass number – atomic number.
  • In a neutral atom, number of electrons = number of protons.

The structure of an atom

The structure of an atom

Electronic Configuration

  • Electrons fill shells in order: first shell holds 2, second holds 8, third holds 8 (simplified model).
  • The electronic configuration is written as numbers separated by commas, e.g., carbon is 2,4.
  • The number of occupied shells equals the period number; the number of outer electrons equals the group number (for Groups I–VII).
  • Elements in the same group have the same number of outer-shell electrons.
  • Noble gases have full outer shells and are unreactive.

A simplified model showing the electron shells

A simplified model showing the electron shells

Isotopes

  • Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
  • They have the same chemical properties because they have the same electron arrangement.
  • Physical properties (e.g., density, melting point) may differ due to different masses.
  • Example: carbon-12 (⁶ protons, ⁶ neutrons) and carbon-14 (⁶ protons, ⁸ neutrons).

The structure of a hydrogen-2 (deuterium) atom

The structure of a hydrogen-2 (deuterium) atom

幻灯片

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练习题

免费预览——53 题中的 8 题。注册即可查看全部。
  1. 1.Which of the following is a pure substance made up of two or more elements chemically combined?

    Easy
    • AElement
    • BCompound
    • CMixture
    • DSolution
  2. 2.What is the relative mass of a proton?

    Easy
    • A0
    • B1
    • C1/1840
    • D2
  3. 3.The atomic number is the number of protons in the nucleus of an atom.

    Easy

    True or false?

  4. 4.What is the electronic configuration of a neutral magnesium atom?

    Easy
  5. 5.An atom of element X has atomic number 29 and mass number 63. How many neutrons does it have?

    Medium
    • A31
    • B37
    • C40
    • D34
  6. 6.Complete the sentence:

    Easy

    Isotopes are atoms of the same element that have the same number of protons but a different number of ____.

  7. 7.Match each subatomic particle to its charge.

    Easy
    • Proton
    • Neutron
    • Electron
    • 1+
    • 0
    • 1-
  8. 8.Arrange the following elements in order of increasing atomic number: chlorine, sodium, carbon, calcium.

    Easy
    • Carbon
    • Sodium
    • Chlorine
    • Calcium

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