General overview (key concepts in Chemistry)

How has the Dalton model of an atom changed over time?

Dalton’s theory was that all things are made of atoms, and they cannot be created, divided or destroyed, atoms join with others to make new substances, atoms of the same element are exactly alike. Thomson discovered that atoms can be divided into smaller parts, and proposed the plum-pudding model, with negative scattered electrons in a positively charged ball. Ernest Rutherford discovered the nucleus and that it was positively charged, the atom was mostly empty space, and that electrons travel in random spaces around the nucleus.

Name the sub-atomic particles, their positions, their masses, and their charges

Proton: found in the nucleus, mass of 1, +1 charge

Neutron: found in the nucleus, mass of 1, no/0 charge

Electron: found in shells, mass of 1/2000, -1 charge

Why do atoms contain equal numbers of protons and electrons?

Atoms are overall neutral, the charge on protons is +1, the charge on electrons is -1. The number of protons is the same as the number of electrons so charges cancel out

What is the mass number of an atom?

The total number of protons and neutrons an atom has

What is an isotope?

Different atoms of the same element with the same number of protons and electrons, but different numbers of neutrons

Why are some atomic masses not whole numbers?

Since isotopes have different number of neutrons, isotopes of the same element have different atomic masses. Relative atomic mass takes an average of abundance of each isotope, which can result in the atomic mass not being a whole number

What is the formula for relative atomic mass?

Relative atomic mass=((mass of isotope x percentage abundance)x number of isotopes)/ 100

How did Mendeleev order his periodic table?

In order of atomic masses, taking into account chemical properties within groups. He left gaps for elements that were yet to be discovered

How did Mendeleev use his table to predict properties of future elements?

He realised that elements with similar properties could be put into groups so he could leave appropriate gaps. Elements with the properties predicted were then later discovered

How does atomic number decide where in the modern periodic table an element is?

Elements are ordered in the size of increasing atomic number. Elements with similar properties are in groups, which also have the same number of electrons in their outer shell, giving them these chemical properties.

How can you identify a metal in the periodic table?

They are found to the left and bottom of the periodic table. Thy lose electrons to form positive ions with the electronic structure of a noble gas

How can you identify a non-metal in the periodic table?

They are found towards the top and right of the periodic table. They gain electrons to form negative ions with the electronic structure like that of a noble gas

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

Group number reveals how many electrons in an element’s outer shell

Period number reveals which shell the outer electrons are in; all shells before the outer shell will be full

How are ionic bonds formed?

Electrons are transferred between atoms. Metals lose electrons to become positively charged (cations). Non metals gain electrons to become negatively charged (anions)

What is an ion?

An atom or group of atoms with a positive or negative overall charge

What ions do elements in groups 1, 2, 6 and 7 form?

Group 1 - lose 1 electron to form +1 ions

Group 2 - lose 2 electrons to form +2 ions

Group 6 - gain 2 electrons to form -2 ions

Group 7 - gain 1 electron to form -1 ions

What does -ate mean in the name of a compound?

There is a negatively charged ion in the compound. There are also three or more elements, one of which is oxygen

What is the lattice structure for ionic compounds?

Regular arrangement of ions, held together by electrostatic forces of attraction between oppositely charged ions

Explain how a covalent bond is formed

A pair of electrons is shared between non-metals

Why do ionic compounds have high melting points?

There are strong electrostatic forces between oppositely charged ions which require lots of energy to overcome

When do ionic compounds conduct electricity?

When they are molten or in solution (aqueous)

Why do ionic compounds sometimes conduct electricity?

When the compound is molten, the ions are charged and now are free to move. This cannot happen in a fixed ionic lattice

Why do simple molecular compounds have low melt in and boiling points?

They have weak intermolecular forces between molecules which requires little energy to overcome

Do simple molecular compounds conduct electricity?

No

Why do giant covalent structures have a high melting point?

Lots of energy is required to break strong covalent bonds

How do metals conduct electricity?

There are electrons which are delocalised and free to move and carry charge among positive ions which are fixed in place

Are metals insoluble in water?

Yes

Structure of graphite

Layers of hexagonal rings of carbon with weak intermolecular forces. There is one delocalised electron per carbon atom, as each carbon atom is bonded to three other carbon atoms

Explain the properties of graphite

Soft: weak intermolecular forces between layers allows layers to slide over each other

Conducts electricity: there is one delocalised electron per carbon atom

Explain the uses of graphite

In electrodes (for electrolysis): conducts electricity, has a high melting point

Lubricants: slippery due to layers being able to slide over each other

Structure of diamond

No delocalised electrons, and all carbon atoms are covalently bonded to four other carbon atoms

Explain the properties of diamond

It is very hard and has a very high melting point. It also doesn’t conduct electricity as it has no charged particles

Why is diamond used in cutting tools?

It is very hard

What is a fullerene?

A molecule made of carbon

Name two fullerenes

Graphene, C60

What are the properties of C60?

It is slippery as it has weak intermolecular forces, it has a low melting point, is spherical, has strong covalent bonds between carbon atoms and a large surface area

Explain the properties of graphene

High melting point: covalent bonds between carbon atoms

Conducts electricity: has delocalised electrons

What is a polymer?

Long chain molecules formed from many monomers (such as poly(ethene))

What are the properties of metals?

High melting point, high density, good conductors of heat and electricity, malleable, ductile and generally shiny

Why are metals malleable?

Atoms are arranged in uniform rows which can slide over each other

Why can metals conduct electricity?

Electrons in the metal are charges that can move

Properties of non metals

Low boiling points, poor conductors of heat and electricity, and brittle

Limitations in representing ionic compounds by a dot and cross diagram

There are no lattice structure or ionic bonds

Limitations of representing ionic compounds by a 2D diagram

Only shows one layer and doesn’t show the formation of ions

Limitations in representing ionic compounds by a 3D diagram

It shows spaces between ions and doesn’t show charges

Limitations of representing covalent molecules by dot and cross diagrams

Doesn’t show relative sizes of atoms, and doesn’t show intermolecular forces

Limitations in representing covalent molecules by a ball and stick diagram

Bonds shown as sticks rather than forces, and it doesn’t show how covalent bonds form

Describe an experiment to work out the empirical formula of magnesium oxide

Weigh a sample of magnesium, heat the sample in a crucible and weigh the mass of magnesium oxide at the end. Calculate the mass of oxygen by finding the increase in mass. Calculate the moles of oxygen using the experimental mass value and the relative atomic mass. Work out the whole number ratio of the number of moles of magnesium to oxygen

Formula for mass (with moles and relative atomic mass)

Mass=moles x relative atomic mass

Formula for concentration

Concentration = mass/volume

Formula for number of particles (with moles and avogadro’s constant)

Number of particles = avogadro’s constant x moles