8th grade atoms, elements and the periodic table

Example

Which particle has a very tiny mass (about 1/1840 of a proton)?

1. Electrons orbit the nucleus in shells, have a −1 charge and almost no mass.
2. So the answer is: electron

Answer: electron

Example

An atom of fluorine is written ¹⁹₉F (mass number 19, atomic number 9). How many neutrons does it have?

1. 19 − 9 = 10
2. So the answer is: 10

Answer: 10

Example

How many atoms in total are in one molecule (formula unit) of sodium hydroxide, NaOH?

1. Na: 1, O: 1, H: 1
2. 1 + 1 + 1 = 3
3. So the answer is: 3

Answer: 3

Example

How many atoms are there altogether in one molecule or formula unit of CH₄?

1. C: 1, H: 4
2. 1 + 4 = 5
3. So the answer is: 5

Answer: 5

Example

Complete the word equation: lithium + water → ? + hydrogen

1. alkali metal + water → metal hydroxide + hydrogen
2. So the answer is: lithium hydroxide

Answer: lithium hydroxide

Example

Chlorine water is added to potassium iodide solution. Will a reaction happen?

1. chlorine is above iodine, so it is more reactive.
2. So the answer is: yes: chlorine displaces iodine

Answer: yes: chlorine displaces iodine

Example

Why are noble gases so unreactive?

1. With a stable full outer shell, noble gases do not need to lose, gain or share electrons.
2. So the answer is: Their outer electron shell is full

Answer: Their outer electron shell is full

Example

Which particle did James Chadwick discover in 1932?

1. Chadwick showed the nucleus contains uncharged neutrons as well as protons.
2. So the answer is: the neutron

Answer: the neutron