Grade 9 Science — Inside the atom
Count protons, neutrons and electrons from an atomic number and a mass number, fill the shells and read off a valency, and say what makes two atoms isotopes.
Name: ________________________
Before you start
The parts of an atom, each one named.
- 1. The center
- 2. The nearest ring
- 3. The middle ring
- 4. The furthest ring
The center is the nucleus, holding the protons and neutrons. The rings are the shells, filled from the inside out: K first, then L, then M.
1.Nitrogen's electronic configuration is 2, 5. What is its valency? Answer with a number.
2.An atom of atomic number 26 has 56 nucleons. How many neutrons has it? Answer with a number.
3.Match each element to its symbol.
- Iron
- Sodium
- Potassium
- Silver
- Gold
- Ag
- Na
- K
- Fe
- Au
4.Put the shells in the order electrons fill them, starting from The K shell, nearest the nucleus.
- The M shell
- The L shell
- The K shell, nearest the nucleus
- The N shell
5.Oxygen's electronic configuration is 2, 6. What is its valency? Answer with a number.
6.Why do the isotopes of an element behave the same way chemically?
- a) They have the same melting and boiling points
- b) They have the same number of electrons, arranged the same way
- c) They have the same mass number
- d) They have the same number of neutrons
7.An atom has 17 protons and 18 neutrons. What is its mass number? Answer with a number.
8.Using the rule that a shell numbered n holds at most 2n² electrons, what is the greatest number the M shell, where n is 3, can hold? Answer with a number.
Answer key — Grade 9 Science — Inside the atom
- 1. 3
- 2. 30
- 3. Iron → Fe; Sodium → Na; Potassium → K; Silver → Ag; Gold → Au
- 4. 1. The K shell, nearest the nucleus 2. The L shell 3. The M shell 4. The N shell
- 5. 2
- 6. b) They have the same number of electrons, arranged the same way
- 7. 35
- 8. 18