Key concepts in chemistry

Question 1

Where are metals located in the periodic table?

Answer 1

On the left side of the table, wiht the dividing line going from under Al to Ts

Question 2

Uncommon formulae

Answer 2

Iodine = I2
Bromine = Br2
chlorine, Cl2
fluorine, F2
oxygen, O2
nitrogen, N2
hydrogen, H2

Question 3

What is a chemical union of two or more elements called?

Answer 3

Compound

Question 4

Define ionic compounds

Answer 4

A compount where atoms are joined together with ionic bonds. Usually contain at least one metal and one non metal.

Question 5

Define ion

Answer 5

An ion is a charged particle when an atom gains or loses electrons

Question 6

Daltons model

Answer 6

Published in 1803, he thought that all matter was made of atoms which he imagined as tiny solid balls. He thought atoms could not broken down any further, the atoms of a given element are identical to eachother, during chemical reactions atoms rearrange to make different substances. Daltons model has changed over time because of the discovery of sub atomic particles.

Question 7

Masses of particles

Answer 7

Proton = 1 
Neutron = 1 
electron = 1/1835

Question 8

Calculating number of subatomic particles rules.

Answer 8

Number of protons = atomic number
Number of electrons = Atomic number
Number of neutrons = mass number - atomic number

Question 9

Define isotopes

Answer 9

Atoms of the same element that have different numbers of neutrons in their nuclei.

Question 10

Mendeleev’s Periodic table

Answer 10

He organised elements in order of increasing relative atomic mass. He noted chemical properties of the elements and their compounds showed a periodic trend. He arranged the elements by putting them with others that had similar chemical properties. He left GAPS for undiscovered elements. He predicted elements that had not been found yet by seeing what would fit next to other elements in the gap

Question 11

Define atomic number.

Answer 11

Number of protons in the nuclei

Question 12

Why do atoms have similar properties when they are in the same group?

Answer 12

The number of electrons on the outer shell is the same, so they are similar.

Question 13

Covalent bonds

Answer 13

When atoms share electrons between them. Usually non metals.

Question 14

Definition of a molecule

Answer 14

A group of two or more atoms joined together by covalent bonds. They will always contain the same number of atoms in each element.

Question 15

Dot and cross diagrams

Answer 15

The outer shell is drawn as a circle - circles overlap when there is a covalent bond. Electrons from one atom are drawn as dots and electrons from the other are drawn as crosses.

Question 16

Giant Covalent structures

Answer 16

Covalent bonding leads to the formation of molecules: these are either simple molecules which contain a set amount of atoms joined by covalent bonds or Giant Covalent substances which contain many atoms joined together by covalent bonds. EG: SILLICA- Main compound found in sand, it is a giant covalent substance.

Question 17

Properties of giant covalent structures

Answer 17

High melting points, Conduction of electricity, Insoluable in water.

Question 18

Diamond and Graphite properties

Answer 18

Different forms of carbon. Joined together by 4 other carbon atoms by covalent bonds. Diamond is a giant covalent substance joined to 4 carbon atoms, tetrahedral network structure and there are no free electrons.

Graphite is also a giant covalent structure- Joined to 3 other carbon atoms, hexagonal layered network, each carbon atom has one un-bonded outer electron.

Question 19

Delocalised electrons

Answer 19

Free to move through the structure of graphite, so graphite can conduct electricity. Makes it useful for electrodes in batteries and for electrolysis. Layers in graphite can slide over one and other as the forces between them are weak.

Question 20

Metals vs Non metals

Answer 20

Metals are on the left hand side of the periodic table - Non metals are on the right. Metals are usually: Shiny, have high melting points, good conductors of electricity and heat, high density and malleable. Non metals: Dull, Low melting points, Poor electicity and heat conductors, low density and brittle

Question 21

Exceptions to the metal/non metal rules

Answer 21

Mercury has a low melting point, graphite has a high melting and boiling point and is a good conductor of electricity

Question 22

Ionic bonds

Answer 22

Metals and non metals - loss and gain of electrons of atoms, ionic lattice structure

Question 23

Simple bonds

Answer 23

Non metals - Shares pairs of electrons between atoms, small group of atoms held together, a molecular structure

Question 24

Giant covalent

Answer 24

Non-Metals
Share pairs of electrons between atoms
Billions of atoms are held together
Giant covalent lattice strucrure

Question 25

Metallic bonds

Answer 25

Metals
Outer electrons free to move
Billions of positive metal ions, giant metallic lattice structure

Question 26

Calculations

Answer 26

Avogadro’s constant - 6.02 x 10^23

Mass in (g) = Mr x Number of moles of mass = Mr x Mol