Chemistry: Test 1

Question 1

What is an atom?

Answer 1

The basic unit of all matter, consisting of protons, neutrons and electrons

Question 2

What are isotopes?

Answer 2

Atoms that have the same number of protons as another but different numbers of neutrons
Same chemical properties but slightly different physical properties

Question 3

What are ionic compounds?

Answer 3

Between a metal and non metal
Transfer of electrons from one species to another, producing charged ions which attract each other with electrostatic interactions
First element if given by its full name while second has its name shortened and -ide is added is added to the end
Use drop and swap method

Question 4

What are covalent compounds?

Answer 4

Between two non metals
Result when atoms share electrons to produce neutral molecules
First element given full name and seconded is shortened with -ide added
Prefixes used to indicate the number of atoms

Question 5

What is an element?

Answer 5

Substances composed of only one type of atom

Question 6

What are compounds?

Answer 6

Composed of two or more different types of elements chemically combined in a fixed proportion

Question 7

What is a mixture?

Answer 7

Two or more substances mixed together in any fixed proportion

Question 8

Sieving

Answer 8

Separation by particle size
Separates a mixture of solids
Involves passing the mixture through mesh
Smaller particles pass through the mesh, leaving larger ones behind

Question 9

Filtration

Answer 9

Separation by particle size
Separates solids from a liquid or gas

Question 10

Gravitational filtration

Answer 10

Uses the weight of the solid liquid mixture to push the mixture through the paper
The purified liquid that is collected is called the filtrate and the solid collected in the filter paper is the residue

Question 11

Vacuum filtration

Answer 11

The solid liquid mixture poured into the funnel is sucked into the flask by a vacuum
The solid residue is trapped by the filter paper

Question 12

Evaporation

Answer 12

Separation by boiling point
Some solids dissolve in liquids to from a solution
Solvent is boiled off to recover solid solute

Question 13

Distillation

Answer 13

Separation by boiling point
Uses the same principles as evaporation but is performed in an apparatus in such a way that the evaporated liquid can be recovered

Question 14

Density

Answer 14

Measure of the mass per unit of volume of a substance
Denser substances will sink and less dense will float

Question 15

Sedimentation

Answer 15

Separation by density
Also known as settling
Form of gravitational separation

Question 16

Decantation

Answer 16

Separation by density
Pouring liquid from sediment

Question 17

Separation funnels

Answer 17

Separation by density
If two liquids have different densities and are immiscible, the the liquids can be separated with a separation funnel
The less dense liquid floats to the top and the denser liquid sinks
When the tap is opened, the denser liquid flows out first

Question 18

Centrifugation

Answer 18

Separation by density
Spinning a mixture rapidly
Denser particles are pushed to the outside of the container

Question 19

What is a heterogenous mixture?

Answer 19

Variable compositions and properties throughout
Possible to identify separate components

Question 20

What are homogenous mixtures?

Answer 20

Uniform composition and properties throughout
Known as a solution

Question 21

What is relative isotopic mass?

Answer 21

Scientific standard for measuring mass
One unit is 1/12 mass of the carbon 12 isotope
Each isotope mass is compared to this standard
Equal to protons + neutrons

Question 22

What is relative atomic mass?

Answer 22

Weighted average of the relative masses of the isotopes of the element relative to carbon 12

Question 23

What is the formula for relative atomic mass?

Answer 23

A = ( % x relative isotopic mass) + ( % x relative isotopic mass) / 100

Question 24

What is mass spectrometry?

Answer 24

Technique used to measure the mass of atoms or molecules
Used to identify the presence and relative abundance of isotopes in a sample

Question 25

How does a mass spectrometer work?

Answer 25

Separates the individual isotopes in a sample
Determines the mass of each isotope
Calculates the relative abundance

Question 26

What are the key operating steps of a mass spectrometer?

Answer 26

1) The sample is vaporised and then ionised using high energy electrons
2) The ions are separated and accelerated according to their mass to charge ratios in an electric or magnetic field
3) The ions that have a particular mass to charge ratio are detected by a device that counts the number of ions that strike it

Question 27

John Dalton

Answer 27

Thought that all matter was made up of these indivisible atoms and that the atoms of different elements had different weights
He further proposed that compound are formed from the combination of the atoms of two or more element in simple ratios
He stated that all atoms of a given element are identical in size and mass

Question 28

Joseph John Thompson

Answer 28

Concluded that particles must be negatively charged and be present in all atoms
Since atoms are electrically neutral, he also proposed that they must contain positive particles
Developed the plum pudding model
Negatively charge particles are spread throughout the positively charged sphere of the atom

Question 29

Bohr model of the atom

Answer 29

Electrons revolve around the nucleus in fixed, circular orbits
The electrons orbits correspond to specific energy levels or shells in the atom
They cannot exist between two energy levels
Larger radii = higher energy

Question 30

What is an electron configuration?

Answer 30

Describes the arrangement of electrons surrounding the nucleus of an atom
Indicates how many electrons are in each energy level or shell

Question 31

Atomic radius

Answer 31

The size of an atom is dependant on the number of electrons in the atom, the shells in which these electrons are located, and the charge on the nucleus of the atom
Atomic radius decreases going across a period, and increases going down a group

Question 32

Ionisation energy

Answer 32

Ionisation energy is the energy required to remove one mole of electrons from one mole of atoms in the gaseous state
The first ionisation energy is the energy required to remove the outermost electron from an atom of an element in the gas phase
Ionisation energy decreases down a group, and increases across a period
Ionisation energy increases across a period and decreases down a group

Question 33

Electronegativity

Answer 33

Electronegativity is the ability of an element to attract electrons in a covalent bond towards itself
The higher the electronegativity, the more strongly that element attracts the shared electron
Decreases down a group, and increases along a period

Question 34

Core charge

Answer 34

The effective positive charge experienced by the valence or outer shell electrons in the atom
Electrons in the inner shells are thought to have a shielding or cancelling effect of the positive charge of the nucleus
Core charge = protons - inner electrons
Core charge increases across a period and stays the same down a group

Question 35

What are valence electrons?

Answer 35

Outermost electrons in an atoms electron shell
Involved in chemical bonding
Atoms with fewer than four valence electrons tend to lose electrons while atoms with more than four valence electrons tend to gain electrons

Question 36

Why does magnesium form cations with a 2+ charge, but chlorine atoms form anions with a 1- charge?

Answer 36

Atoms react to achieve a more stable electron configuration, and achieve the octet rule
Magnesium has two valence electrons and is likely to lose them, resulting in a two positive charge (as there are twelve protons but ten electrons)
Chlorine has seven valence electrons and is likely to gain one, resulting in a one negative charge (as there are eight electrons and seven protons)

Question 37

What is the electronegativity of group 18?

Answer 37

As noble gases do not from compounds with other elements, they do not have electronegativity

Question 38

Why would you expect an ionised atom to be in a gaseous state?

Answer 38

There is very little attraction between other particles which affects the ionisation energy

Question 39

Explain the periodicity in the ionisation energy of atoms

Answer 39

It varies in a repetitive way as you move through the Periodic Table.

Question 40

What is the relationship between ionisation energy and metal or non metal properties?

Answer 40

The greater the ionisation energy the greater the non-metallic character
Metals are electron accepting and non-metals are electron donating

Question 41

Electrostatic separation

Answer 41

Objects that have opposite electric charges attract each other
The forces of attraction between opposite charges is known as the electrostatic force
Electrostatic filters use the electrostatic force to separate solid particles from a gas

Question 42

Why does atomic radius increase as you move along a period?

Answer 42

As the number of protons increase, the attraction on the valence electrons increase, pulling the electrons closer to the nucleus

Question 43

Earnest Rutherford

Answer 43

Fired a beam of positively charged alpha particles at a very thin sheet of gold foil
Most of the alpha particles passed straight through
Although, a few were deflected and bounced back
Concluded that most of the atom must be empty space, to allow the alpha particles to move through it
Most of the mass and it’s positive charge must he located in a tiny, central region
Thought the electrons orbited around the nucleus, like the planets and the sun