the structure of the atom

Question 1

what is an atom

Answer 1

the basic particles of a chemical element

Question 2

what are the subatomic particles of an atom

Answer 2

neutron
proton
electrons

Question 3

where are the subatomic particles found

Answer 3

neutrons and protons are found in the nucleus
electrons are found in different energy levels (shells) around the nucleus

Question 4

what is the charge of the subatomic particles

Answer 4

neutron - 0 (neutral)
proton - +1 (positive)
electron - -1 (negative)

Question 5

what is the relative mass of the subatomic particles

Answer 5

neutron - 1
proton - 1
electron - 0.00055 (very small, nearly

Question 6

why are atoms neutral overall

Answer 6

the number of protons equal the number of electrons so the opposite charges cancel eachother out

Question 7

what is the mass number

Answer 7

the number of protons and neutrons

Question 8

what is the atomic number

Answer 8

the number of protons (=no. of electrons)

Question 9

what are isotopes

Answer 9

atoms of the same element with the same number of protons but different number of neutrons
they have the same atomic number but different mass numbers

Question 10

chlorine seems to have 18.5 neutrons but there is no such thing as half a neutron. how can this be explained?

Answer 10

atoms of the same element are not identical. they can have a different mass. this is because the number of neutrons in the nucleus can vary. the mass number is therefore a weighted average.

Question 11

does the number of protons and electrons change in an isotope

Answer 11

they do not change

Question 12

how are isotopes usually written

Answer 12

with the symbol followed by the mass number

Question 13

what does it mean if an atom has a higher number of neutrons

Answer 13

the mass is greater and this changes the physical properties slightly

Question 14

what is relative isotopic mass

Answer 14

the mass of an isotope of an atom compared with one twelfth of the mass of an atom of carbon-12

Question 15

what is relative atomic mass

Answer 15

the weighted mean mass of one atom of an element compared with one twelfth of the mass of an atom of carbon-12

Question 16

what is empirical formula

Answer 16

it shows the simplest whole number ratio of each type of atom

Question 17

how do we calculate empirical formula

Answer 17

• write each mass in g
• write each atomic mass
• find the number of moles (mass/mr)
• divide by the smallest number
• check for whole numbers and write the formula

Question 18

O=16, S=32
an oxide of sulphur contains 50% sulphur and 50% oxygen by mass. work out its empirical formula for 100g of the compound

Answer 18

1) mass in g - sulphur =50 and oxygen =50
2) Ar - S=32 and O=16
3) no. of moles - 50/32 = 1.5625 and 50/16 = 3.125
4) divide by the smallest number - 1.5625 /1.5625 = 1 3.125/1.5625 = 2
5) check for whole numbers and write the formula - SO2

Question 19

H=1 C=12 O=16
a 2.3g sample of compound X contains 1.2g carbon, 0.3g of hydrogen and 0.8g of oxygen. work out its empirical formula

Answer 19

1) carbon = 1.2g, hydrogen = 0.3g and oxygen = 0.8g
2) carbon = 12, hydrogen = 1 and oxygen = 16
3) 1.2/12 = 0.1, 0.3/1=0.3 and 0.8/16= 0.05
4) 0.1/0.05=2, 0.3/0.05=6 and 0.05/0.05 = 1
5)C2H30