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What is the kinetic theory of solids?
Solids have a fixed volume and shape and they have a high density.
The atoms vibrate in position but can’t change location
The particles are packed very closely together in a fixed and regular pattern
What is the kinetic theory of liquids?
Liquids also have a fixed volume but adopt the shape of the container
They are generally less dense than solids (an exception is water), but much denser than gases
The particles move and slide past each other which is why liquids adopt the shape of the container and also why they are able to flow freely
What is the kinetic theory of gases?
Gases do not have a fixed volume, and, like liquids, take up the shape of the container
Gases have a very low density
Since there is a lot of space between the particles, gases can be compressed into a much smaller volume
The particles are far apart and move randomly and quickly (around 500 m/s) in all directions
They collide with each other and with the sides of the container (this is how pressure is created inside a can of gas)
What are the state changes?
Melting
Freezing
Boiling
Evaporation
Condensation
What is melting?
Melting is when a solid changes into a liquid
Requires heat energy which transforms into kineticenergy, allowing the particles to move
Occurs at a specific temperature known as the melting point (m.p.)
What is freezing?
Freezing is when a liquid changes into a solid
This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same. Water, for example, freezes and melts at 0 ºC
Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature
What is boiling?
Boiling is when a liquid changes into a gas
Requires heat which causes bubbles of gas to form belowthe surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid
Occurs at a specific temperature known as the boiling point (b.p.)
What is evaporation?
Evaporation occurs when a liquid changes into a gas and occurs over a range of temperatures
Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid's surface at low temperatures, below the b.p. of the liquid
The larger the surface area and the warmer the liquid surface, the more quickly a liquid can evaporate
What is condensation?
Condensation occurs when a gas changes into a liquid on cooling and it takes place over a range of temperatures
When a gas is cooled its particles lose energy and when they bump into each other they lack the energy to bounce away again, instead they group together to form a liquid
How does state changes and particles correlate?
When substances are heated, the particles absorb thermal energy which is converted into kinetic energy
Heating a solid causes its particles to vibrate more
As the temperature increases, the particles vibrate so much that the solid expands until the structure breaks
This is when the solid melts into a liquid
Heating a liquid causes its particles to move more and spread out
Some particles at the surface gain sufficient energy to overcome the intermolecular forces
This is when a liquid starts to evaporate
When the boiling point is reached, all of the particles gain enough energy to escape and the liquids boils into a gas
What affects volume in gases?
A change in temperature or pressure?
How is pressure created with gases?
Gas particles are in constant and random motion, the pressure that a gas creates in a closed container is produced by the gaseous particles hitting the container walls
How does temperature affect the volume of a gas?
Increasing temp increases kinetic energy which causes more collisions
What is diffusion
The movement of particles from an area of high concentration to an area of low concentration
How does molecular mass affect diffusion?
Gases with a lower relative molecular mass area lighter, which means they travel faster and further in same amounts of time
What makes up substances?
Elements, compounds and mixtures
What is an element
A substance made of atoms that all contain the same number of protons and cannot be split into anything simpler
What is a compound?
A pure substance made up of two or more elements chemically combined, they cannot be separated into their elements by physical means
What is a mixture?
A combination of two or more substances (elements and/or compounds) that are not chemically combined
they can be separated by physical methods such as filtration or evaporation
What make up atoms?
Protons, electrons and neutrons
What is located in the nucleus?
Protons and neutrons
What is the charge and relative mass of a proton?
The relative mass is 1 and charge is +1
What is the charge and relative mass of a neutron?
The relative mass is 1 and charge is neutral
What is the charge and relative mass of a electro?
The relative mass charge is 1/1840 (negligible) with a charge of -1
How do you calculate how many protons are in an atom?
Number of protons = mass number – number of neutrons
How do you calculate how many electrons are in an atom?
An atom is neutral and therefore has the same number of protons and electrons
How do you calculate how many neutrons are in an atom?
Number of neutrons = mass number – number of protons
What is an isotope?
Isotopes are different atoms of the same element that contain the same number of protons but a different number of neutrons
Why don’t isotopes share the same physical characteristics?
Isotopes display the same chemical characteristics
This is because they have the same number of electrons in their outer shells, and this is what determines their chemistry
The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only
The difference in mass affects the physical properties, such as density, boiling point and melting point
What is an ion?
an electrically charged atom or group of atoms formed by the loss or gain of electrons
What is a negative ion called?
An anion, formed when gaining electrons
What is a positive ion called?
A cation, formed when losing an electron
Whats the relationship between metals and ions?
All metals lose electrons to other atoms to become positively charged ions
Whats the relationship between non metals and ions?
All non-metals gain electrons from other atoms to become negatively charged ions
What is ionic bonding?
Ionic compounds are formed when metal atoms react with non-metal atoms
Metal atoms lose their outer electrons which the non-metal atoms gain to form positive and negative ions
The positive and negative ions are held together by strong electrostatic forces of attraction between oppositecharges
What is a dot and cross diagram?
Dot and cross diagrams are diagrams that show the arrangement of the outer-shell electrons in an ionic or covalent compound or element
The electrons are shown as dots and crosses
In a dot and cross diagram:
Only the outer electrons are shown
The charge of the ion is spread evenly which is shown by using brackets
The charge on each ion is written at the top right-hand corner
what is a lattice structure?
Lattice structure refers to the arrangement of the atoms of a substance in 3D space
In lattice structures, the atoms are arranged in an orderedand repeating fashion
The lattices formed by ionic compounds consist of a regular arrangement of alternating positive and negative ions
What structures do ionic compounds have?
they have a giant lattice structure
What are properties of ionic compounds?
Ionic compounds are usually solid at room temperature
They have high melting and boiling points
Ionic compounds are good conductors of electricity in the molten state or in solution
They are poor conductors in the solid state
Why do ionic compounds have high melting and boiling points?
They have giant structures
There are strong electrostatic forces of attraction between oppositely charged ions in all directions
The forces need lots of energy to overcome them
Why are ionic compounds poor conductors when solid?
The ions are in fixed positions in the lattice
They are therefore unable to move and carry a charge
Why are ionic compounds good conductors when molten or in a solution?
When the ionic compound is melted or dissolved in water, the ions are able to move and carry a charge
What is a covalent bond?
They are formed when pairs of electrons are shared between atoms, only non metal elements participate in this.
Why do covalent bonds have low melting and boiling points?
They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules
These forces are very weak when compared to the covalent bonds and so most small molecules are either gases or liquids at room temperature
As the molecules increase in size the intermolecular forces also increase as there are more electrons available
This causes the melting and boiling points to increase
Why are covalent bonds poor conductors of electricity?
They are poor conductors of electricity as there are no free ions or electrons to carry the charge.
Most do not conduct at all in the solid state and are thus insulators
What are the allotropes formed from carbon?
Diamond and graphite
What is the structure of graphite?
Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom which becomes delocalised
The covalent bonds within the layers are very strong, but the layers are attracted to each other by weakintermolecular forces
What is an allotrope?
Different atomic or molecular arrangements of the same element in the same physical state
What is the structure of diamond?
In diamond, each carbon atom bonds with four other carbons, forming a tetrahedron
All the covalent bonds are identical, very strong and there are no intermolecular forces
What are the properties and uses of graphite?
Graphite conducts electricity
Each carbon atom is bonded to three others leaving one free electron per carbon atom
These free (delocalised) electrons exist in between the layers
They are free to move through the structure and carry charge
Graphite has a high melting point
Graphite has a giant covalent structure
There are strong covalent bonds between the carbon atoms
These need lots of energy to break
Graphite is slippery
Graphite is arranged in layers
Although the atoms within the layers are joined by strong covalent bonds, the layers have only weak intermolecular forces between them
As a result the layers can slide over each other
This property allows graphite to be used in pencils and as an industrial lubricant
What are the properties of diamond?
Diamond does not conduct electricity
All the outer shell electrons in carbon are held in the four covalent bonds around each carbon atom
As a result, there are no freely moving particles to carry a charge
Diamond has a very high melting point
Diamond has a giant covalent structure
There are strong covalent bonds between the carbon atoms
These need lots of energy to break
It is extremely hard and dense
It has strong covalent bonds and each carbon atom is bonded to four other carbon atoms
Diamond's hardness makes it very useful in cutting tools like drills
Diamond has the following physical properties:
It does not conduct electricity
It has a very high melting point
It is extremely hard and dense
What is silicon (IV) oxide?
It is a macromolecular compound which occurs naturally as sand and quartz
Each oxygen atom forms covalent bonds with 2 silicon atoms and each silicon atom in turn forms covalent bonds with 4 oxygen atoms
A tetrahedron is formed with one silicon atom and four oxygen atoms, similar to diamond
SiO2 has lots of very strong covalent bonds and no intermolecular forces so it has similar properties to diamond
It is very hard, has a very high boiling point, is insoluble in water and does not conduct electricity
SiO2 is cheap since it is available naturally and is used to make sandpaper and to line the inside of furnaces
What is the structure of a metal?
Metals consist of giant structures
Within the metal lattice, the atoms lose their outer electrons and become positively charged metal ions
The outer electrons no longer belong to any specific metal atom and are said to be delocalised
This means they can move freely between the positive metal ions and act like a “sea of electrons”
The metallic bond is the strong force of attraction between the positive metal ions and the delocalised electrons
This type of bonding occurs in metals and metal alloys, which are mixtures of metal
Most metals have high melting and boiling points
There are strong electrostatic forces of attraction between the positive metal ions and the negative delocalised electrons within the metal lattice structure
These needs lots o energy to be broken
Metals are good conductors of heat and electricity
The delocalised electrons are free to move and carry a charge through the whole structure
Most metals are malleable
This means they can be hammered into shape
This is because the atoms are arranged in layers which can slide over each when force is applied
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