Grade 10 chemisty Inorganic Chemistry – The Atom Structure of the atom Notes
Inorganic Chemistry — The Atom: Structure of the Atom
Subject: Chemistry | Topic: Inorganic Chemistry | Subtopic: The Atom — Structure of the atom (target age: 15)
- Understand energy levels and orbitals (s and p) for the first 20 elements.
- Understand and explain isotopes and isotope notation.
- Determine relative atomic mass (RAM) from isotopic abundances.
- Write electron arrangement using s and p notation for elements 1–20.
- Develop interest in studying atomic structure through activities and simple models.
1. Quick summary — What is an atom?
An atom is the smallest part of an element that still has the element's chemical properties. It has a tiny central nucleus (protons + neutrons) and electrons moving around the nucleus in energy levels (shells). Protons are positive, electrons negative, neutrons neutral.
2. Energy levels (shells) and orbitals
- Energy levels are labelled n = 1, 2, 3, … Each level has subshells called s, p, d, f. For the first 20 elements we only need s and p subshells.
- Maximum electrons per shell (simple model): n=1 → 2; n=2 → 8; n=3 → 18 (but for elements 1–20 we use up to 8 in n=3 before 3d fills).
- Subshell capacities: s = 2 electrons, p = 6 electrons.
3. s and p orbitals (shapes and simple pictures)
one lobe, holds 2 e−
two lobes, each p subshell has 3 orbitals → total 6 e−
4. Electron arrangements (s and p notation) — Elements 1 to 20
Below each element: atomic number (Z) and electron configuration using s and p notation.
| # | Element | Z | Electron arrangement (s, p) |
|---|---|---|---|
| 1 | H | 1 | 1s1 |
| 2 | He | 2 | 1s2 |
| 3 | Li | 3 | 1s2 2s1 |
| 4 | Be | 4 | 1s2 2s2 |
| 5 | B | 5 | 1s2 2s2 2p1 |
| 6 | C | 6 | 1s2 2s2 2p2 |
| 7 | N | 7 | 1s2 2s2 2p3 |
| 8 | O | 8 | 1s2 2s2 2p4 |
| 9 | F | 9 | 1s2 2s2 2p5 |
| 10 | Ne | 10 | 1s2 2s2 2p6 |
| 11 | Na | 11 | 1s2 2s2 2p6 3s1 |
| 12 | Mg | 12 | 1s2 2s2 2p6 3s2 |
| 13 | Al | 13 | 1s2 2s2 2p6 3s2 3p1 |
| 14 | Si | 14 | 1s2 2s2 2p6 3s2 3p2 |
| 15 | P | 15 | 1s2 2s2 2p6 3s2 3p3 |
| 16 | S | 16 | 1s2 2s2 2p6 3s2 3p4 |
| 17 | Cl | 17 | 1s2 2s2 2p6 3s2 3p5 |
| 18 | Ar | 18 | 1s2 2s2 2p6 3s2 3p6 |
| 19 | K | 19 | 1s2 2s2 2p6 3s2 3p6 4s1 |
| 20 | Ca | 20 | 1s2 2s2 2p6 3s2 3p6 4s2 |
5. Isotopes and notation
Isotopes are atoms of the same element (same Z) with different numbers of neutrons (different mass number A). Notation: A X (or written X–A). Example: Carbon-12 is 12C (6 protons, 6 neutrons), Carbon-13 is 13C (6 protons, 7 neutrons).
Relative atomic mass (RAM) — how to calculate
RAM is the weighted average mass of an element's isotopes, using their relative abundances:
RAM = Σ (isotope mass × fractional abundance)
Suppose natural chlorine is 75% 35Cl and 25% 37Cl (these are simple example abundances):
- Fractional abundance 35Cl = 0.75, mass = 35
- Fractional abundance 37Cl = 0.25, mass = 37
RAM = (35 × 0.75) + (37 × 0.25) = 26.25 + 9.25 = 35.50
This is why chlorine on the periodic table shows ≈ 35.5.
6. How these points meet the learning outcomes
- (a) Describe the structure of the atom — nucleus, electrons, shells, orbitals explained and pictured.
- (b) Determine RAM — formula and worked example given so learners can practise with other isotopic data.
- (c) Write electron arrangement — full list for first 20 elements using s and p notation provided.
- (d) Develop interest — activities and simple models suggested below to make learning practical and fun.
7. Suggested learning experiences (for classroom / home)
- Make atom models: Use clay, beads, or bottle caps to build nucleus and shells for H → Ca. Label protons, neutrons, electrons.
- Electron-configuration race: In groups, give each group element cards and ask them to write s/p configurations; fastest correct group wins.
- Isotope & RAM activity: Give different isotope masses/percentages (real or made-up). Learners calculate RAM and compare with periodic table values (use chlorine and carbon examples).
- Draw orbitals: Sketch 1s, 2s, 2p and label number of electrons. Discuss how p orbitals are three directions (px, py, pz) — total 6 electrons in p subshell.
- Use phones or school computers: Interactive periodic table apps or simulations (search for "PhET atom building") to visualise atoms and orbitals.
- Short quiz / exit ticket: Ask three short questions: e.g., write 1s2 2s2 2p3 → which element? (Answer: N); calculate RAM for given isotopes; draw p orbital shape.
- Homework: Write electron configuration for elements 11–20 and explain what an isotope is using a Kenyan example (e.g., carbon in organic matter).
8. Short practice questions (with answers)
- Write the electron configuration of oxygen. (Answer: 1s2 2s2 2p4)
- What is an isotope? Give one example. (Answer: same Z different neutrons; e.g., 35Cl and 37Cl)
- Calculate RAM: isotope A mass 10 (60%), isotope B mass 11 (40%). RAM = ? (Answer: 10×0.60 + 11×0.40 = 6.0 + 4.4 = 10.4)
- How many electrons can the 3p subshell hold? (Answer: 6)