Grade 9 Atoms & Electrons worksheet
from Gradelings · Name: ______________________
How to explain it
- Atomic number = number of protons. A neutral atom has the same number of electrons.
- Shells hold 2, then 8, then 8 electrons for the first 20 elements. Outer-shell electrons are valence electrons.
- Ions form when atoms gain or lose electrons. Isotopes have different numbers of neutrons.
Example: Magnesium has atomic number 12. How are its electrons arranged in shells? A neutral atom has 12 electrons. Fill 2, then 8, then the rest: 12 − 10 = 2. Answer: 2, 8, 2
Question 1
Argon (Ar) has atomic number 18. How many electrons does a neutral atom of it have?
answer box
18
Hint: In a neutral atom, the number of electrons equals the number of protons, which is the atomic number.
Question 2
In the periodic table, elements in the same column (group) have…
- the same colour
- the same mass
- the same number of protons
- similar chemical properties, because they have the same number of valence electrons
similar chemical properties, because they have the same number of valence electrons
Hint: Valence electrons control how an atom reacts.
Question 3
How many electron shells (energy levels) are used by a neutral sodium atom?
- 2
- 3
- 5
- 4
3
Hint: Sodium has 11 electrons arranged 2-8-1, so 3 shells are in use.
Question 4
In the periodic table, a period (row) tells you…
- the element's state at 0 °C
- the number of electron shells in the atom
- the colour of the element
- the number of neutrons
the number of electron shells in the atom
Hint: Elements in the same row have the same number of occupied shells.
Question 5
Group 1 elements, the alkali metals, are very reactive because they have…
- one valence electron that is easily lost
- no neutrons
- a full outer shell
- eight valence electrons
one valence electron that is easily lost
Hint: Losing one electron gives them a stable arrangement.
Question 6
How many electron shells (energy levels) are used by a neutral carbon atom?
- 3
- 2
- 4
- 1
2
Hint: Carbon has 6 electrons arranged 2-4, so 2 shells are in use.
Question 7
Metals are generally…
- always magnetic
- gases at room temperature
- brittle and poor conductors
- good conductors of electricity and malleable
good conductors of electricity and malleable
Hint: Metals can be shaped without breaking and let electrons flow.
Question 8
When an atom loses an electron, it becomes…
- a different element
- an isotope
- a negative ion
- a positive ion
a positive ion
Hint: Fewer electrons than protons gives a positive charge.
Question 9
Helium (He) has atomic number 2. How many electrons does a neutral atom of it have?
answer box
2
Hint: In a neutral atom, the number of electrons equals the number of protons, which is the atomic number.
Question 10
Which particle is found in the nucleus and has a positive charge?
- proton
- neutron
- electron
- photon
proton
Hint: Protons are positive. Neutrons are neutral. Electrons are negative and orbit outside.
Answer key
- 1. 18
- 2. similar chemical properties, because they have the same number of valence electrons
- 3. 3
- 4. the number of electron shells in the atom
- 5. one valence electron that is easily lost
- 6. 2
- 7. good conductors of electricity and malleable
- 8. a positive ion
- 9. 2
- 10. proton
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