key concepts in chemistry

Question 1

Describe how the Dalton model of an atom has changed over
time because of the discovery of subatomic particles

Answer 1

Dalton said that atoms were solid spheres and made up of elements, but Thomson’s experiment showed that the charge and mass of an atom must contain even smaller negatively charged particles - electrons
now called a plum pudding model

Question 2

Describe the structure of an atom

Answer 2

an atom is made up of neutron, electrons, protons.
neutrons and protons are in the nucleus, with electrons surrounding them in shells

Question 3

Recall the relative charge of a proton

Answer 3

+1

Question 4

Recall the relative charge of a neutron

Answer 4

0

Question 5

Recall the relative charge of an electron

Answer 5

-1

Question 6

recall the relative mass of a proton

Answer 6

1

Question 7

recall the relative mass of a neutron

Answer 7

1

Question 8

recall the relative mass of an electron

Answer 8

0.0005/ negligible

Question 9

Explain why atoms contain equal numbers of protons and electrons

Answer 9

charge on electrons is the same size and charge of protons, but the opposite so the charges cancel out

Question 10

Describe the nucleus of an atom as very small compared to the overall size of the atom

Answer 10

most of the mass of the atom is concentrated in the nucleus so compared to the overall size of the atom, the nucleus is tiny

Question 11

where is most of the mass in an atom

Answer 11

most of the mass in an atom is concentrated in its nucleus

Question 12

what does mass number mean

Answer 12

total number of protons and neutrons in the atom

Question 13

Describe atoms of a given element as having the same number
of protons in the nucleus and that this number is unique to that
element

Answer 13

atoms in an element have the same number of protons in the nucleus
isotopes are forms of the same element which have the same number of protons but a different number of neutrons

Question 14

what is an isotope

Answer 14

isotopes are different forms of the same element which have the same number of protons but a different number of neutrons
(in their nuclei)

Question 15

how to calculate number of protons, neutrons and electrons given the atomic number and mass number

Answer 15

mass number = number of protons and electrons
atomic number = number of protons
atoms has the same number of protons as electrons
to work out neutrons do atomic number - mass number

Question 16

mass number =

Answer 16

total number of protons and neutrons (bigger number)

Question 17

atomic number =

Answer 17

number of protons only

Question 18

Explain how the existence of isotopes results in relative atomic
masses of some elements not being whole numbers

Answer 18

1. if an element has more than one isotope

its Ar is the average of the mass numbers of all the different isotopes so it might not be a whole number

Question 19

Ar =

Answer 19

(relative atomic mass)
the Ar of an element is the average mass of one atom of the element compared to 1/12 of the mass of one atom of carbon-12

Question 20

how to calculate relative atomic mass of an element from the masses and abundances of its isotopes
(ex boron 10 and boron 11are isotopes of Boron, the relative abundances of boron 10 and 11 are 4 and 16, work out the Ar of boron)

Answer 20

1. multiply each relative isotopic mass by its relative abundance and then add up the results

((104) + (1116) = 216)

2. divide this by the sum of the isotopic abundances

(216 / (16+4) = 10.8

3. to check if your right, your number should be in between the isotopes number

Question 21

Describe how Dmitri Mendeleev arranged the elements, known
at that time, in a periodic table by using properties of these
elements and their compounds

Answer 21

• he based the elements based on their properties and the properties of their compounds
• he put elements with similar chemical properties in columns
• sometimes he switched the order of elements so he could keep the same properties in the same columns

Question 22

Describe how Dmitri Mendeleev used his table to predict the
existence and properties of some elements not then discovered

Answer 22

• he left gaps to keep elements with similar chemical properties together
• columns with gaps were used to predict properties of undiscovered elements

Question 23

Explain that Dmitri Mendeleev thought he had arranged
elements in order of increasing relative atomic mass but this
was not always true because of the relative abundance of
isotopes of some pairs of elements in the periodic table

Answer 23

Mendeleev thought he had organised the elements in order of increasing atomic mass
but this wasn’t always true because at the time he was unaware of the isotopes and their relative abundances

Question 24

Explain the meaning of atomic number of an element in terms
of position in the periodic table and number of protons in the
nucleus

Answer 24

• atomic number = number of protons only
• periodic table is ordered with elements in ascending atomic mass

Question 25

describe the periodic table

Answer 25

1. elements are arranged in order of increasing atomic number
2. rows are called periods
3. elements with similar chemical properties are placed in the same vertical columns
4. columns are called groups

Question 26

Identify elements as metals or non-metals according to their
position in the periodic table

Answer 26

• metals = groups 1 and 2
• non-metals = group 6,7 and 0
• the group number corresponds to number of electrons it has in its outer shell

Question 27

Predict the electronic configurations of the first 20 elements in
the periodic table as diagrams and in the form

Answer 27

1. circles in electronic configuration is period number in periodic table
2. number of electrons in outermost shell is shown by group number of periodic table
3. number of electrons in all the shells of an element is shows by atomic number
   *electronic configurations go in the form 2.8.8
   (where these are all full shells)

Question 28

how to work out number of circles in electronic configuration from periodic table

Answer 28

• period number

Question 29

how to work out number of electrons in the outermost shell

Answer 29

group number in periodic table