Chemistry: Atomic Structure, Bonding, Reactions and Acids
What this domain covers
Grade 10 Chemistry tests atomic structure, periodic table patterns, ionic and covalent bonding, formulae and balanced equations, acids, bases and salts, and simple reaction rates. Questions often ask you to explain patterns rather than just recall names.
Core rules and concepts
- An atom has protons and neutrons in the nucleus and electrons in shells. Atomic number equals the number of protons. Mass number equals protons plus neutrons. Ions form when atoms gain or lose electrons.
- In the periodic table, group number relates to outer-shell electrons and period number to shells. Group 1 metals lose one electron; group 7 non-metals gain one; group 0 gases have full outer shells and are unreactive.
- Ionic bonding occurs between metals and non-metals by electron transfer. Covalent bonding occurs between non-metals by sharing electrons.
- A balanced equation has the same number of each type of atom on both sides. You may change coefficients, never subscripts in a correct formula.
- Acids have pH below 7, alkalis above 7, and pH 7 is neutral. Acid + base -> salt + water. Indicators show acidity or alkalinity by colour change.
Worked example
Explain the formula of sodium chloride. Sodium has electron arrangement 2,8,1. It loses one electron to form Na+ with arrangement 2,8. Chlorine has 2,8,7 and gains one electron to form Cl- with 2,8,8. The oppositely charged ions attract strongly, and because one Na+ balances one Cl-, the formula is NaCl, not Na2Cl. The reasoning depends on electron transfer and charge balance, not on the number of atoms in the original shells.
Traps that cost marks
Do not confuse a coefficient with a subscript: 2H2O contains 4 hydrogen atoms and 2 oxygen atoms. pH 7 is neutral, not acidic. A dilute acid is not necessarily a weak acid. Never balance an equation by changing a formula such as H2O to H2O2. Show state symbols only when asked or when they clarify the reaction.