10th grade atoms, elements and the periodic table

Question 1

An element has two isotopes: mass 47 (40 %) and mass 49 (60 %). What is its relative atomic mass? Give 1 decimal place.

Answer 

Question 2

The count rate of a radioactive source falls from 960 counts/min to 240 counts/min in 16 minutes. What is its half-life, in minutes?

Answer min

Question 3

Calculate the relative formula mass (Mr) of calcium hydroxide, Ca(OH)₂. Relative atomic masses: Ca = 40, O = 16, H = 1.

Answer 

Question 4

Which type of radiation: no charge and no mass?

• A. alpha (α)
• B. beta (β)
• C. gamma (γ)

Question 5

Why is the relative atomic mass of chlorine 35.5 and not a whole number?

• A. It is an average of its isotopes, weighted by abundance
• B. It is measured badly
• C. Electrons add 0.5
• D. Chlorine atoms have half a neutron

Question 6

What is the charge on a magnesium ion?

• A. +2
• B. +3
• C. −1
• D. −2

Question 7

Bonding: which statement is NOT true?

• A. Diamond is a giant covalent structure and is very hard.
• B. Simple covalent substances such as water have low melting and boiling points.
• C. Ionic compounds have high melting points.
• D. Solid sodium chloride conducts electricity.

Question 8

Nuclear radiation: which statement is NOT true?

• A. We can predict exactly when a particular nucleus will decay.
• B. Gamma rays are part of the electromagnetic spectrum.
• C. Background radiation comes from natural and man-made sources.
• D. Alpha radiation is the most dangerous if the source is inside the body.

Question 9

A sample has an activity of 1200 Bq. Its half-life is 8 days. What is its activity after 32 days, in Bq?

Answer Bq

Question 10

What type of bonding is in potassium bromide (KBr)?

• A. ionic
• B. covalent
• C. metallic

Question 11

Calculate the relative formula mass (Mr) of MgO. Relative atomic masses: Mg = 24, O = 16.

Answer 

Question 12

Natural copper contains 69 % of mass 63 and 31 % of mass 65. Calculate its relative atomic mass to 1 decimal place.

Answer 

Question 13

Why are gamma rays used to sterilise medical equipment in sealed packs?

• A. They make the equipment radioactive
• B. They are stopped by plastic
• C. They pass through the packaging and kill microbes
• D. They heat the equipment to 1000 °C

Question 14

A sample contains 3200 undecayed nuclei. How many remain undecayed after 3 half-lives?

Answer 

Question 15

What is the percentage by mass of chlorine in HCl? Relative atomic masses: H = 1, Cl = 35.5. Give 1 decimal place.

Answer %

Question 16

An element has two isotopes: mass 72 (40 %) and mass 74 (60 %). What is its relative atomic mass? Give 1 decimal place.

Answer