1.1 Structure of the atom

• Structure of the atom: protons, electrons and neutrons
• Atomic number and mass number of elements
• Electron arrangement of the first 20 elements
• Energy level diagrams using dots
• Metals and non-metals from outer electrons

• describe the structure of the atom
• determine the mass number of elements
• draw the electron arrangement in atoms using dot diagrams
• classify elements into metals and non-metals
• show interest in classifying elements into metals and non-metals

“How is the structure of the atom important?”

The titles are open to everyone. Reading a lesson needs an account — sign in or create one.

1. Atom, element and particle
   40 min · 1 practice tasks · quiz
   A particle is a tiny bit of matter. An atom is the smallest particle of an element. An element is one kind of atom, such as carbon in charcoal.
2. The proton: positive, in the nucleus
   40 min · 1 practice tasks · quiz
   A proton has charge +1, sits in the nucleus, and has relative mass about 1. The proton count tells you which element you have.
3. The neutron: no charge, in the nucleus
   40 min · 1 practice tasks · quiz
   A neutron has charge 0, sits in the nucleus, and has relative mass about 1. It adds mass without adding charge. Hydrogen has no neutron; helium has two.
4. The electron: negative, on shells
   40 min · 1 practice tasks · quiz
   An electron has charge -1, occupies shells around the nucleus, and has tiny relative mass (about 1/1840). Lithium shows two inner electrons and one outer.
5. The nucleus is protons plus neutrons
   40 min · 1 practice tasks · quiz
   The nucleus at the centre holds protons and neutrons and nearly all the mass. Electrons stay on shells. Carbon-12: 6 protons, 6 neutrons, electrons 2.4.
6. Atomic number Z is the number of protons
   40 min · 1 practice tasks · quiz
   Atomic number Z equals the number of protons. It tells you which element the atom is. Hydrogen Z=1, carbon Z=6, sodium Z=11. First 20 elements only; no periodic table.
7. Mass number A is protons plus neutrons
   40 min · 1 practice tasks · quiz
   Mass number A equals protons plus neutrons. Neutrons = A minus Z. Sodium: Z=11, A=23, so 12 neutrons. Electrons are not added into A.
8. In a neutral atom, electrons equal protons
   40 min · 1 practice tasks · quiz
   A neutral atom has equal numbers of electrons and protons, so overall charge is zero. Oxygen: Z=8 so 8 electrons, arranged 2.6.
9. Energy levels fill 2, then 8, then 8, then 2
   40 min · 1 practice tasks · quiz
   For the first 20 elements, electrons fill energy levels to a maximum of 2, 8, 8, then 2. Fill from the inside. Calcium is 2.8.8.2, not 2.8.10.
10. Arrangements of carbon, oxygen, sodium and chlorine
    40 min · 1 practice tasks · quiz
    Carbon 2.4 (charcoal), oxygen 2.6 (air and water), sodium 2.8.1 and chlorine 2.8.7 (table salt). Count electron dots on each concentric shell.
11. Dot diagrams: nucleus, rings, then dots
    40 min · 1 practice tasks · quiz
    Energy level diagrams in this course use dots, not crosses. Draw the nucleus, concentric shells, then place electron dots on the rings. Sodium 2.8.1 is the worked method.
12. Metals: few outer electrons
    40 min · 1 practice tasks · quiz
    Among the first 20, metals have 1, 2 or 3 outer electrons. Use Na, Mg, Al, K and Ca. Skip iron: Z=26 is outside the first 20. Aluminium sufurias; sodium in salt.
13. Non-metals: more outer electrons, or a full shell
    40 min · 1 practice tasks · quiz
    Non-metals in the first 20 have four or more outer electrons, or a full outer shell. Carbon, nitrogen, oxygen, fluorine, sulphur, chlorine and neon. Charcoal is carbon. Neon is 2.8.
14. Practise the first 20: hydrogen to calcium
    40 min · 1 practice tasks · quiz
    Use the list hydrogen to calcium: state Z, write the arrangement 2 / 2.8 / 2.8.8 / 2.8.8.2, and classify metal or non-metal from outer electrons. No periodic table.