2.1.1 atomic structure and isotopes

Question 1

Definition of Atomic number

Answer 1

The number of protons in an elements nucleus.

Question 2

Definition of Atomic mass

Answer 2

The number of protons and neutrons added to together.

Question 3

Definition of relative isotopic mass

Answer 3

The mass of an isotope relative to 1/12th of the mass of an atom of carbon-12.

Question 4

Definition of relative atomic mass

Answer 4

The weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12.

Question 5

Definition of an isotope

Answer 5

An isotope is an atom of the same element with the same number of protons but a different number of neutrons and therefore different masses.

Question 6

What are the relative charges and masses of the 3 types of sub-atomic particle?

Answer 6

Proton 1+ relative charge, relative mass of 1
Neutron 0 relative charge, relative mass of 1
Electron 1- relative charge, relative mass of 1/1836

Question 7

Why do isotopes have the same chemical properties, but different physical properties?

Answer 7

The mass of an isotope determines its physical properties and the electrons determine the chemical properties. As an isotope has the same number of electrons it will have the same chemical properties no matter how many neutrons it has.

Question 8

What is an ion?

Answer 8

An ion is a charged atom.

Question 9

What are the two different types of ion?

Answer 9

Cation- positively charged, has fewer electrons than protons.
Anion- negatively charged, has more electrons than protons.

Question 10

How are ions shown?

Answer 10

Ions are shown with their charge, to show that they are ions.

Question 11

What is the unit for relative isotopic mass?

Answer 11

Relative isotopic mass has no units because it is a ratio of 2 masses.

Question 12

How do you determine the relative atomic mass?

Answer 12

Mass spectrometers are used to find out the percentage abundance of each isotope and the relative isotopic mass of each isotope. From this you can use an equation to work out the relative atomic mass.

Question 13

How do you work out the relative atomic mass?

Answer 13

Step 1: Use the percentage abundance and multiply by the mass-to-charge ratio of each isotope. E.g. For Chlorine 35 and 37 are the mass-to-charge ratios.
Step 2: add these two numbers together.
Step 3: divide the number from the previous calculation by 100, so that it is no longer a percentage.

Question 14

Name the diatomic molecules.

Answer 14

H2, N2, O2, F2, Cl2, Br2 and I2.

Question 15

What are the state symbols and why are they used?

Answer 15

(g) gas
(l) liquid
(s) solid
(aq) aqueous/ dissolved in water

They are used to indicate physical change in chemical reactions.

Question 16

What is meant by the term empirical formula?

Answer 16

The empirical formula is the simplest whole number ratio of atoms of each element in a compound.

Question 17

Why is an empirical formula important?

Answer 17

An empirical formula is important for substances that do not exist as small molecules. These can be metals or non-metals such as silicon, carbon and ionic compounds like NaCl.

Question 18

What is the equation that links moles, mass and molar mass?

Answer 18

n=m÷M
n= amount of substance moles
m= mass
M= molar mass

Question 19

Volume measurements.

Answer 19

1cm3= 1ml
1dm3= 1000cm3=1000ml=1l

Question 20

How do you convert between moles and solution volumes?

Answer 20

n=c x V
n= amount of substance, moles
c= concentration, moldm3-
V= volume dm3

When using cm3 as volume the equation changes to

n= c x (V ÷ 1000)

Question 21

How do you work out standard solution?

for example, how much of x is required to prepare y cm3 of a z moldm3 standard solution?

Answer 21

Step 1: work out the moles required by using
n= c x (V ÷ 1000).
Step 2: work out the molar mass e.g molar mass of H2O is 18.0
Step 3: rearrange the formula n=m ÷ M to calculate the mass of x required

Question 22

What is an ionic bond?

Answer 22

The electrostatic attraction between ions.

Question 23

How do you find the number of particles in a substance?

Answer 23

N= n x Na

N= number of particles 
n= amount of substance (mol)
Na= Avogadro's constant

Question 24

How do you find the amount of substance in mol?

Answer 24

n= N ÷ Na

n= amount of substance
N= number of particles
Na= Avogadro's constant