Key Concepts in Chemistry: SC3 + SC4

Question 1

Describe how Mendeleev arranged the elements in the periodic table.

Answer 1

• In order of increasing relative atomic mass.
• Left gaps for undiscovered elements.
• In matching physical and chemical properties.

Question 2

Who made the periodic table?

Answer 2

Dmitri Mendeleev

Question 3

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

Answer 3

He left gaps for undiscovered elements.

Question 4

Explain the meaning of atomic number of an element

Answer 4

The atomic number is the number of proton in the nucleus of an atom.

Question 5

Describe the properties of metals

Answer 5

• Metals are malleable.
• insoluble in water
• high melting and boiling points
• Good conductors of heat and electricity

Question 6

Define electron configuration

Answer 6

The way in which an atom’s electrons are arranged in its shells

Question 7

What also happens if the elements in the periodic table are arranged in increasing atomic number?

Answer 7

• Elements with similar properties are in the same column/ group
• Non-metals are on the right of the table
• metals are on the left side of the table

Question 8

What is common about the electron shells for the first twenty elements?

Answer 8

• first shell can contain up to 2 electrons
• second and third shell can contain up to 8 electrons

Question 9

Explain why atoms contain equal numbers of protons and electrons

Answer 9

They have equal numbers of positive and negative charges, and so are neutral overall.

Question 10

How is the electron configuration related to the position of an element on the periodic table?

Answer 10

• the number of shells there are in an electronic configuration of an element is represented in the periodic table as the period number that the element is situated in
• The number of electrons in the outermost shell of an element is represented in the periodic table as the group number that the atom is in
• the number of electrons in an atom is the same as its atomic number unless it is an ion
• In the first twenty elements, the first and innermost shell will only have 2 electrons max

Question 11

What did Dalton’s theory claim?

Answer 11

• All matter is made up of tiny particles called atoms
• Atoms are tiny, hard spheres that are indivisible
• atoms of different elements are different from each other
• Compounds are combinations of different elements
• atoms of an element are identical to each other
• during chemical reactions, atoms rearrange to form different substances
  —> Therefore, they cannot be destroyed
• all atoms in an element are identical

Question 12

What is the relative charge of a proton?

Answer 12

+1

Question 13

What is the relative charge of a neutron?

Answer 13

0

Question 14

What is the relative charge of an electron?

Answer 14

-1

Question 15

What is the mass of a proton?

Answer 15

1

Question 16

What is the mass of a neutron?

Answer 16

1

Question 17

What is the mass of an electron?

Answer 17

negligible/ 1/2000

Question 18

How have Dalton’s ideas been disproven?

Answer 18

Subatomic particles mean that atoms are divisible

Question 19

Describe the structure of an atom.

Answer 19

A nucleus containing protons and neutrons, surrounded by electrons in shells

Question 20

What is the mass number of an atom?

Answer 20

The total amount of protons and neutrons in the nucleus.

Question 21

Why doesn’t an atom have an overall charge?

Answer 21

Both the protons and electrons are of an equal number and so the charges cancel each other out

Question 22

Who discovered the atom’s nucleus?

Answer 22

Ernest Rutherford

Question 23

Describe Rutherford’s experiment which allowed him to discover the atom’s nucleus

Answer 23

• Fired alpha particles at a thin gold foil
• expected that all of them would pass through
• Some were deflected
• those that were deflected were had said to hit the nucleus
• but majority passed through indicating that atoms are mainly empty space

Question 24

Define ‘atomic mass’

Answer 24

The average mass of all the isotopes in an element

Question 25

What is a group on the periodic table?

Answer 25

A vertical column of elements with the same number of outer shell electrons

Question 26

What is a period on the periodic table?

Answer 26

A row of elements with the same number of electron shells

Question 27

Define isotopes

Answer 27

Atoms of an element with the same number of protons and electrons but a varying number of neutrons

Question 28

What is the standard isotope?

Answer 28

Carbon 12

Question 29

What is the equation for the relative atomic mass?

Answer 29

((% of isotope 1 x mass of isotope 1) + (% of isotope 2 + mass of isotope 2))/ the number of atoms

Question 30

Where is most of the mass of the atom concentrated in?

Answer 30

The nucleus of the atom

Question 31

Why do atoms of different elements vary?

Answer 31

They have different amounts of protons in their nucleus, which changes their physical properties

Question 32

Why isn’t the relative atomic mass of many elements a whole number?

Answer 32

It is the average of all the atoms in an element, which means that the average isn’t always a whole number

Question 33

What are valence electrons?

Answer 33

Electrons on the outmost shell which are involved in reactions

Question 34

What is the average atomic radius?

Answer 34

0.1 nm (1 x 10^-10 m)

Question 35

What is the average atomic nucleus radius?

Answer 35

10,000 times smaller than an atom (1 x 10^-14 m)

Question 36

Who discovered the ‘plum pudding’ model of the atom?

Answer 36

JJ Thompson

Question 37

What is the plum pudding model of the atom?

Answer 37

Atoms are balls of positively charge with negative electrons embedded in it

Question 38

What is the nuclear model of the atom?

Answer 38

Atoms are made of a small positive nucleus orbited by negative electrons.

Question 39

What were the problems with the nuclear model of the atom?

Answer 39

Model claimed that electrons orbited the nucleus but didn’t explain why

Question 40

What did JJ Thompson discover?

Answer 40

The electron

Question 41

What were the problems with the plum pudding model?

Answer 41

Model didn’t have a nucleus

Question 42

How did Bohr modify the Nuclear model?

Answer 42

• stated electrons moved around the nucleus in orbit of fixed sizes and energies
• the energies of the electron were quantized so they couldn’t occupy values of energy between fixed levels

Question 43

What were the problems with Bohr’s modifications?

Answer 43

• They didn’t work with heavier atoms
• Moving electrons should emit energy and collapse into the nucleus

Question 44

What is the quantum model of the atom?

Answer 44

• Schrödinger claimed that electrons don’t move in set paths, but waves
• he also said it was impossible to know the exact location of an electron at any given time
• instead suggested the ‘cloud of probability’ called orbitals in which we are likely to find an electron

Question 45

Who discovered neutrons?

Answer 45

James Chadwick