Key Terms In Chemistry Flashcards
JJ Thompson’s Plum Pudding Theory
Positively charged sphere
With electrons that are negatively charged atoms
Rutherfords Model
Tiny positively charged nucleus at the centre
Surrounded by a cloud of negative electrons
Most of the atom is empty space
Gold Leaf Test - Rutherford
Fired positively charged alpha particles at a thin gold sheet.
Most particles went straight through, some were deflected and a small number were backwards- so the plum pudding could not be right
Bohr’s Model
Electrons only exist in fixed orbits or shells
Each shell has a fixed energy
Protons
- relative mass
- relative charge
Heavy and positively charged
Relative Mass - 1
Relative Charge - +1
Found in the nucleus which is positively charged
Neutrons
Heavy Neutral Relative mass - 1 Relative charge - 0 Found in nucleus
Electrons
Negative
Relative mass- 0.0005
Relative Charge - -1
Found in electron shells
Atomic number
Tells you how many protons and electrons there are in the atom
Mass number
Tells you the total number of protons and neutrons in an atom
Isotopes
Different forms of the same element, which have the same number of protons but a different number of neutrons.
How do you calculate the relative atomic mass from isotopic abundances?
Multiply each relative atomic mass by its isotopic abundance and add up the results
Divide by the sum of the abundance’s
How did the order of the periodic table come about?
Dmitri Mendeleev arranged them based on their properties, then realised they were in order of atomic mass
What do periods show in the periodic table?
Represent a new full shell of electrons
What do groups show on the periodic table?
Corresponds to the number of electrons it has on its outer shell
Ions
Ions are charged particles- when atoms lose or gain electrons to form ions
When do negative atoms form?
Anions - when atoms gain electrons- they have more electrons than protons so they are negatively charged
When do positive ions form?
Cations- when atoms lose electrons - they have more protons than electrons - they are positively charged
Group 1 and 2 ions
They are metals so they lose electrons to form positive ions
Group 6 and 7 ions
Non metals that gain electrons to form negative ions
Ionic bonding
When a metal and non metal react together
- the metal atoms loses electrons to form a positive ion
- the non metal gains these to form a negative ion
What are oppositely charged ions attracted to each other by?
They are strongly attracted to one another by electrostatic forces this is called an ionic bond
Ionic compound shapes
Always have a giant ionic lattice structures. The ions form a closely packed regular lattice
There are very strong electrostatic forces of attraction between oppositely charged ions in all directions
Ionic compound properties
-melting and boiling points
High melting and boiling points due to the strong attraction between the ions. It takes a large amount of energy to overcome this attraction.
Ionic compound properties
-conductor of electricity?
Solid ionic compounds don’t conduct electricity because the ions are in a fixed place and can’t move.
But when an ionic compound melts, the ions are free to move and can carry an electric current.
Ionic compound properties
- dissolvable?
Many dissolve easily in water. The ions separate and are all free to move in the solution- so they’ll carry and electric current.
Advantages of models that show ionic compound structures
2D representations of molecules are simple and great at showing what atoms contain and how they are connected.
Dot and cross diagrams- show how compounds are formed
3D models show the arrangement of ions
Disadvantages of models that show the structure of ionic compounds
2D representations don’t show the shape of the substance or the size of atoms
Dot and cross diagrams don’t show the size or how they are arranged
3D models only show the outer layer of the substance
Covalent Bonding
Is a strong bond that forms when a pair of electrons is shared between two atoms
What are simple molecular substances made up of?
They are made up of molecules containing few atoms joined by covalent bonds
Properties of simple molecular substances
- bonds
- forces of attraction
Atoms are held together by very strong covalent bonds
The forces of attraction are very weak
Properties of simple molecular substances
- melting and boiling points
- what substance are they at room temperature?
To melt or boil, you only need to break the weak intermolecular forces - melting and boiling points are very low
Most molecular substances are liquid or gas at room temp
Properties of simple molecular substances
- the bigger the molecules the…?
- conducts electricity?
As molecules get bigger, the strength of the intermolecular forces increases, so more energy is needed to break them - melting and boiling points increase
-don’t conduct electricity as they don’t contain any free electrons or ions
Polymers
How are they formed?
Are molecules made up of long chains of covalently bonded carbon atoms
-they are formed when lots of small molecules called monomers join together
Giant covalent structure properties
- bonds
- melting and boiling points
All atoms are bonded together by strong covalent bonds
Very high melting and boiling points as lots of energy is needed to break the covalent bonds
Giant covalent structure properties
- conductor of electricity?
- soluble?
Don’t contain charged particles - don’t conduct electricity
Aren’t soluble in water
Diamond - giant covalent structure
- how many covalent bonds?
- melting points?
Made up of a network of carbon atoms that each form four covalent bonds
Strong covalent bonds take lots of energy to break- high melting point
Diamond - giant covalent structure
- lattice structure
- conductor of electricity?
Strong covalent bonds hold the atoms in a rigid lattice structure- making diamonds really hard
Doesn’t conduct electricity - no free electrons or ions
Graphite - Giant covalent structures
- how many covalent bonds?
- how strong are the layers?
- what properties does graphite have?
Each carbon atoms forms three covalent bonds- creating sheets of carbon atoms arranged in hexagons
No covalent bonds between layers- weakly held together so they are free to move over each other
- this makes graphite soft and slippery
What is diamond used for?
Used to strengthen cutting tools- as it is really hard as it has a rigid lattice structure
What is graphite used for?
Lubricating material as it’s soft and slippery as the layers can move over each other
Graphite- giant covalent structures
- melting points
- conductor of electricity?
High melting point - covalent bonds need lots of energy to break
Only three out of carbons four electrons are used in bonds- so each carbon atom has one delocalised electron and can move.
- so it conducts electricity
Graphene- giant covalent structure
- what is it?
- how many atoms thick?
A type of fullerene- one layer of graphite
Sheet of carbons are joined to together in hexagons
Sheet is one atom thick- making 2 dimensional
Fullerenes
Are molecules of carbon shaped like closed tubes or hollow balls
What are fullerenes made up of?
Carbon atoms arranged in hexagons
What are fullerenes used for?
Can be used to cage other molecules. Fullerenes structure forms around another atom or molecule which is then trapped inside.
This could be used to deliver a drug directly to cells in the body
How could fullerenes large surface area help?
They could help make a great industrial catalysts - individual catalyst molecules could be attached to the fullerenes
What is metallic bonding?
Electrons in the outer shell of metal atoms are delocalised. There are strong forces of electrostatic attraction between the positive ions and the shared negative electrons
What do the forces of attraction do? Metallic bonding
They hold the atoms together in a regular structure and are known as metallic bonding
What are metals physical properties?
-melting and boiling points
Electrostatic forces between the metal ions and delocalised sea of electrons are very strong, so need lots of energy.
High melting and boiling points - metals are generally shiny
What are metals physical properties?
-dense?
Metals are more dense as ions in the metallic structure are packed closely together.
What are some physical properties of metals?
- malleable?
Malleable - layers of atom in a pure metal can slide over each other- they can be hammered or rolled into small sheets
What are some physical properties of metals?
-conductor of electricity and heat?
The delocalised electrons carry electrical current and thermal energy through the material- so metals are good conductors of heat and electricity
Dot and cross diagram
Is used to explain what happens when a bond is formed. It uses dots and crosses to represent the electrons in different atoms
Properties of simple molecular structures - covalent
Simple molecules
Low melting and boiling points
Some are soluble
Don’t conduct electricity
Monomers
Small , simple molecules that can be joined to make polymers
Properties of monomers
Small chain
Small forces
Low energy
Low melting points
Properties of polymers
More forces
Long chain
More energy
High melting points
Allotropes
Are different structural forms of the same element
Properties of non metals
Insulators
Liquids, gas and solids
Low and high melting points
Brittle
Why are metals malleable?
Force is applied to metals, the regularly arranged ions are free to move over one another. Ions are still held together by delocalised electrons so they do not break
Why do metals conduct electricity?
The delocalised electrons are free to move. This means when a potential difference is applied, the electrons flow in one direction.
Symbol equations must always be…
Balanced and there must always be the same number of atoms of each element on both sides of the equation.
State symbol (s)
Solid
State symbol (l)
Liquid
State symbol (g)
Gas
State symbol (aq)
Aqueous
What does aqueous mean?
Dissolved in water
Formula for water
H20
Formula for carbon dioxide
CO2
Formula for ammonia
NH3
Formula for hydrogen
H2
Formula for chlorine
Cl2
Formula for oxygen
O2
Formula for ion ammonia
NH+
4
Formula for hydroxide ion
OH-
Formula for ion nitrate
NO-
3
Formula for carbonate ion
CO. 2-
3
Formula for sulfate ion
SO. 2-
4
Ionic equations method
Look at the balanced equation
Any ions or aqueous things break up into ions
Take out any aqueous ions that are present on both sides of the equation
Oxidising
Provides oxygen which allows other materials to burn more fiercely
Environmental hazard
Harmful to organisms and the environment
Toxic
Can cause death if swallowed, breathes in or absorbed by skin
Harmful
Can cause irritation, reddening of the skin and blistering
Flammable
Catches fire easily
Corrosive
Destroys materials inc,using living tissues
Steps for risk assessment questions
State the hazard symbol each chemical is
Explain what it means
Explains ways to reduce risk
What was different about how Mendeleev thought he arranged the periodic table?
He thought he has arranged elements in order of increasing relative atomic mass but this was not always true because of the relative abundance’s of isotopes of some pairs of elements in the periodic table
What are elements in the same columns?
Similar properties
What are elements placed in rows?
In atomic order
