Atomic structure and equations
Clear notes with worked examples, then 4 practice questions with answers. Written by Beyond Tutors tutors for the KS3 National Curriculum.
Inside the atom
Nucleus: protons (+1) and neutrons (0). Shells: electrons (−1).
Atomic number = number of protons. Neutral atom: protons = electrons.
The periodic table
Group 1 (alkali metals): very reactive, react with water to make hydrogen. More reactive going DOWN.
Group 7 (halogens): reactive non-metals. Less reactive going down.
Group 0 (noble gases): unreactive, full outer shells.
Balancing equations
Same number of each atom on both sides; change only the big numbers in front.
(4 H and 2 O each side)
REACTIVITY SERIES (most → least)
potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, copper, silver, gold
The atmosphere
78% nitrogen, 21% oxygen, about 1% argon, about 0.04% carbon dioxide.
More traps more heat → global warming.
Practice questions
Try each one, then tap to see the answer and why.
- Question 1 · Atomic structure
An atom has 11 protons. How many electrons does a neutral atom of it have?
- A11
- B0
- C12
- D23
Show the answer
A: 11
Neutral atoms have equal numbers of protons and electrons.
- Question 2 · Atomic structure
Which particles are found in the nucleus of an atom?
- AElectrons only
- BProtons and neutrons
- CProtons and electrons
- DNeutrons and electrons
Show the answer
B: Protons and neutrons
The nucleus holds protons and neutrons; electrons orbit in shells.
- Question 3 · Periodic table
Group 1 metals (e.g. sodium) are stored in oil. Why?
- AThey are too heavy
- BThey react quickly with air and water
- CThey melt easily
- DThey are radioactive
Show the answer
B: They react quickly with air and water
Alkali metals react vigorously with oxygen and water.
- Question 4 · Atomic structure
What is the charge on an electron?
- A+1
- B
- C0
- D+2
Show the answer
B:
Protons are +1, neutrons 0, electrons −1.