Read the core explanations from Electrical Charges in Atoms before testing yourself from memory.
1. The Electrical Charges in Atoms
Every atom contains three types of particles, and each carries a different electrical charge. Understanding these charges is the key to explaining why atoms behave the way they do in chemical reactions.
The relative charges are what matter for understanding atomic behaviour. Protons have a charge of +1, electrons have a charge of -1, and neutrons are neutral with 0 charge.
2. Why Atoms Have No Overall Charge
Here's the crucial rule: in any atom, the number of electrons always equals the number of protons. This isn't a coincidence - it's what makes atoms electrically neutral.
Think of it like a balance. If you have 6 protons (each +1), you need exactly 6 electrons (each -1) to cancel out the positive charge. The result? Zero overall charge.
Worked example: Calculating Overall Charge in a Carbon Atom
A carbon atom has 6 protons and 6 electrons. What is its overall charge?
- 6 protons × (+1) = +6 — Each proton contributes +1 to the total charge
- 6 electrons × (-1) = -6 — Each electron contributes -1 to the total charge
- (+6) + (-6) = 0 — Positive and negative charges cancel out completely
Answer: Overall charge = 0 (neutral atom)
This balance is what keeps atoms stable. If an atom gains or loses electrons, it becomes an ion with a net charge. You will use this idea later in the topic when you study ions and bonding.
3. Atomic Number - The Element's Identity Card
The atomic number is the most important number for any element. It tells you exactly how many protons are in the nucleus, and this number never changes for a particular element.
Carbon always has 6 protons. Oxygen always has 8 protons. Sodium always has 11 protons. Change the number of protons, and you change the element completely.
Since atoms are neutral, the atomic number also tells you the number of electrons. Carbon (atomic number 6) has 6 protons and 6 electrons. Oxygen (atomic number 8) has 8 protons and 8 electrons.
4. Comparing Different Elements
What makes hydrogen different from helium? Or carbon different from nitrogen? It's all about the number of protons in the nucleus.
Worked example: Comparing Hydrogen and Helium Atoms
Compare the atomic structure of hydrogen (atomic number 1) and helium (atomic number 2).
- Hydrogen: 1 proton, 1 electron, 0 neutrons — Atomic number 1 means 1 proton, so 1 electron for neutrality
- Helium: 2 protons, 2 electrons, 2 neutrons — Atomic number 2 means 2 protons, so 2 electrons for neutrality
- Helium has 1 more proton and 1 more electron than hydrogen — This extra proton makes helium a completely different element
Answer: Different elements have different numbers of protons, which determines their chemical properties
This is why the periodic table is arranged by atomic number. Each step up adds one more proton (and one more electron) to create the next element.
5. Exam Technique and Common Mistakes
Examiners love testing your understanding of electrical charges in atoms. Here's how to avoid the common traps and pick up full marks.
Exam language: When describing why atoms are neutral, use the phrase "equal numbers of protons and electrons" rather than just saying "they cancel out".
Exam precision note: when asked about charge, state the charge on each subatomic particle first, then explain how the total positive and negative charges compare. For neutral atoms, equal numbers of protons and electrons give an overall charge of zero.
Mass number is the total number of protons and neutrons in the nucleus. Once you know the mass number and the atomic number, you can calculate neutrons using neutrons = mass number - atomic number.