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melting
Solid → liquid
boiling / evaporating
Liquid → gas
condensing
Gas → liquid
freezing
Liquid → solid
solid properties
- Have a fixed shape
- Do not flow
- High density
LIquid properties
- Flow easily
- Fixed volume but will flow to fit shape of container
gas properties
- No fixed volume or shape
- Less dense than same volume of solid or liquid
Solid structure
- Particles arranged regularly and packed closely together, Vibrate in fixed positions, Strong forces between particles, Small amount of kinetic energy
Liquid Structure
- Particles are mostly touching with some gaps, Particles move about at random, Medium forces between particles, Moderate amount of kinetic energy
Gas structure
Particles move at random and quickly, Particles are far apart, Weak forces between particles, High amount of kinetic energy, Collide with each other and sides of container
Draw the structure of a solid, liquid and a gas
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Describe what happens when water vapour cools to form liquid water
- Particles lose kinetic energy
- Particles move closer together
- Particles move slower and less randomly
Describe what happens when liquid water boils to form water vapour
- Particles gain kinetic energy
- Particles move further apart
- Particles move quicker and more randomly
Describe what happens when liquid water cools to form ice
- Particles lose kinetic energy
- Particles move closer together
- Particles move slower and less randomly
Describe what happens when ice melts to form liquid water
Particles gain kinetic energy and vibrate more
Particles move further apart as forces of attraction are overcome -Particles move quicker and more randomly
How does evaporation occur?
when high-energy particles escape from the liquid's surface, lowering the average kinetic energy. In a closed container, evaporation and condensation happen simultaneously.
what curve is this
Heating curve
what happens to the volume of a gas when its temperature increases
Volume of gas increases
Use kinetic theory to explain why the volume of a gas increases when temperature increases
Particles gain kinetic energy
Particles move quicker and more randomly
Particles move further apart
what happens to the pressure of a gas in a container when its temperature increases
Pressure increases
Use kinetic theory to explain why pressure in a container increases when temperature increases
When particles have more kinetic energy, they move faster and collide with the container walls more forcefully and more frequently. (pressure = force ÷ area)
why do faster-moving particles hit the container walls with more force?
Faster-moving particles have GREATER momentum, so when they collide with the container walls, they exert more force. This is because force = change in momentum/time
What happens to the pressure of a gas in a container when the volume decreases
Pressure increases
Use kinetic theory to explain why pressure in a container increases when volume decreases
at constant temperature, the average kinetic energy of gas particles is constant. In a smaller container, they collide with the walls more frequently, causing an increase in pressure.
Define diffusion
Net movement of particles from an area of high concentration to low concentration
Which factors affect the rate of diffusion?
- Molecular mass [Mr] (The lower the mass of its particles, rate up) - Temperature (The greater the temperature, the greater the kinetic energy of the particles, rate up)
How can diffusion be demonstrated experimentally?
Soaked cotton wool with(NH₃) and (HCl) is placed at opposite ends of a sealed tube. A white ring of NH₃ forms closer to the HCl end, showing that NH₃ diffuses faster due to lower Mr.
element
A substance which contains one TYPE of atom only and Cannot be split into anything simpler by any chemical means
compound
A substance made up of two or more elements chemically combined
mixture
A substance made up of two or more elements NOT chemically bonded together
difference between compound and mixture
chemical bonds
Examples of mixture
soup, blood, air
What is a pure substance?
Contains one type of material only (e.g. one type of element or molecule)
Describe the melting and boiling points of pure substances
Fixed (e.g. boiling point of pure water is exactly 100°C and melting point of pure water is exactly 0°C)
Describe the melting and boiling points of mixtures
Melt and boil over a range of temperatures
atom
Smallest particle of a chemical element that can exist
molecule
Two or more atoms chemically bonded together
Structure of an atom
- Central nucleus containing neutrons and protons
- Surrounded by shells of electrons
Give the relative charge and mass of a proton, neutron and electron
Relative charge= 1, 0, -1
Relative mass= 1, 1, 1/1836
atomic number
number of protons
mass number/nucleon number
total number of protons and neutrons
How is the number of protons in an atom calculated?
atomic number
How is the number of electrons in an atom calculated?
Atomic number
How is the number of neutrons in an atom calculated?
Mass number – atomic number
How many electrons can fit in each electron shell?
2 in the first shell
8 in all other shells
Give the electron configuration of a) Carbon, b) Magnesium, c) Potassium
- Carbon: 2.4
- Magnesium: 2.8.2
- Potassium: 2.8.8.1
How to identify the group number of the periodic table?
number of electrons in the outer shell
Why do elements in the same group have similar chemical properties?
Same number of electrons in outer shell
Why are noble gases (group VIII) unreactive?
- They have a full outer shell of electrons
- Stable
What does the period number of the periodic table tell you?
number of electron shells
isotope
Atoms of the same element with the same number of protons but different number of neutrons
relative atomic mass (Ar)
The average mass of the isotopes of an element compared with 1/12th of the mass of an atom of 12C
Why do isotopes of the same element have the same chemical properties?
- Have same number of electrons
- Have same electron configuration
Ar formula
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A naturally occurring sample of the element chlorine contains 75% of the Cl-35 isotope and 25% of the Cl-37 isotope. Calculate the relative atomic mass of chlorine.
35.5
How is an ion formed?
An atom loses or gains electrons
- Loses electron → forms positive ion (cation)
- Gains electron → forms negative ion (anion)
All ions
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ionic bond
Strong electrostatic force of attraction between oppositely charged ions (Form between a metal and a non-metal)
Dot and cross diagram for Nacl and mgf2
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Give the properties of giant ionic lattices
- High melting and boiling points
- Conduct electricity when molten/dissolved in aqueous solution
- Brittle
Brittle
When the material breaks easily with little or no bending
Why do ionic structures have high melting and boiling points?
- Form giant ionic lattices, Strong electrostatic forces of attraction between oppositely charged ions, Requires lots of energy to break
Why don’t ionic substances conduct electricity when solid?
- Ions are held tightly in fixed positions
- Not free to move
Why do ionic substances conduct electricity when molten/dissolved?
Ions are free to move and Can carry electric charge
Explain why ionic substances are brittle
- Applying force causes ions to move
- Like charges align and repel
- Lattice structure breaks apart
covalent bond
a pair of electrons shared between two atoms
Explain what is a covalent bond
strong electrostatic forces of attraction between nuclei(+)and shared pair of electrons(-), Form between two non-metals, Result in noble gas electron configurations (full outer shell of electrons)
methane, ammonia, oxygen, ethane (dot and cross diagrams)
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simple molecular substance
Small, covalently bonded molecule (e.g. H2O, CO2)
properties of simple molecular compounds
- Low melting and boiling points
- Poor electrical conductivity
Define intermolecular force
Temporary weak attraction between different molecules
Why do simple molecular substances have low melting points?
- Weak intermolecular forces of attraction
- Do not require a lot of energy to overcome
Why does the boiling point of simple molecular substances increase with increasing relative molecular mass?
Boiling overcomes the intermolecular forces of attraction between molecules. Greater Mr = greater intermolecular forces of attraction to be overcome. More heat energy needed to overcome the forces.
Why don’t simple molecular substances conduct electricity?
They have no free-moving charged particles (ions or delocalized electrons) and Their molecules are electrically neutral (No overall electric charge)
Define giant covalent structure
Large lattice of covalently bonded atoms [macromolecules] (- e.g. graphite, diamond, silicon dioxide)
allotrope
Different forms of the same element
Give 2 allotropes of carbon
- Diamond
- Graphite
Why does diamond have such a high melting point?
- Giant covalent structure
- Each carbon atom covalently bonded to 4 others
- Many strong covalent bonds, Require lots of energy to break
Why is diamond used in cutting tools?
Very hard & very high melting point. Every carbon atom forms four strong covalent bonds to nearby carbon atoms. (No weak intermolecular forces)
Why don’t most covalent substances conduct electricity?
- No free electrons
- Each electron in outer shell is bonded
Why doesn’t diamond conduct electricity?
- No free electrons
- Each electron in outer shell is bonded
Why does graphite have such a high melting point?
- Many strong covalent bonds
- Require lots of energy to break
Why does graphite conduct electricity?
- Each carbon atom is only bonded to 3 others
- 4th electron free to move and carry charge
- Graphite can therefore be used as an electrode
Why is graphite used as lubricant?
- Carbon atoms are arranged in layers, Layers held together by weak intermolecular forces (Do not require a lot of energy to break), Layers slide over each other
Describe the structure of silicon(IV) oxide (silicon dioxide)
- Each silicon atom bonds covalently to 4 oxygen atoms
- Each oxygen atom bonds to 2 silicon atoms
- Giant structure
draw diamond and graphite
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Draw silicon (iv) oxide
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What are the similarities in chemical properties between diamond and silicon(IV) oxide?
Giant covalent structures with many strong covalent bonds, requiring lots of energy to break, and each atom forms four covalent bonds.
Consequence of not having free electrons or ions
not being able to carry charge
What are the similarities in physical properties between diamond and silicon(IV) oxide?
Physical properties: They have very high melting points, are hard, and cannot conduct electricity as they have no free electrons or ions to carry a charge.
metallic bond
Electrostatic forces of attraction between positive metal ions and ‘sea’ of delocalised electrons
Why are metals good conductors of heat?
- Delocalised electrons
- As electrons are free to move, heat energy is transferred throughout structure
how do delocalised electrons transfer heat throughout structure?
As heat is applied, these electrons gain energy to move freely and collide with ions, spreading kinetic energy rapidly using ions and other delocalised electrons.
Do only metals have delocalised electrons?
No, other do too ( e.g. graphite)
metals
elements that lose electrons to form positive ions (cations) and have a giant metallic structure
non-metals
elements that gain or share electrons to form negative ions (anions) or covalent bonds
Why do metals conduct electricity?
Delocalised electrons are Free to move
Why do metals have high melting and boiling points?
- Strong electrostatic forces of attraction between positive metal ions and delocalised electrons which Requires a lot of energy to break
Why are metals malleable?
Layers of ions can slide over each other
Why are metals ductile?
Layers of ions can slide over each other
