Chemistry Term 1 Flashcards
What are the three different states of matter?
gas, liquid, solid
Describe the arrangement and movement of particles in gas
- Particles are far apart and have low densities
- Gas particles move very rapidly and in random directions
Describe the arrangement and movement of particles in liquid
- Particles are close together and are more dense than gas
- Particles move slowly and at random
Describe the arrangement and movement of particles in solid
- Particles are close together and like liquids, are denser than gases
- Particles vibrate only in fixed positions
State properties of a solid
- Solids have a fixed shape and cannot flow as particles cannot move from place to place.
- Solids cannot be compressed or squashed as the particles are close together and have no space to move into
- Increasing the temp. causes the particles to vibrate quicker
State properties of a liquid
- A liquid is a pure substance and should not be confused with a solution
- Liquids flow and take the shape of their container as the particles a can move around each other
- Liquids cannot be compressed or squashed as the particles are close together and have no space to move into
State properties of a gas
- Gases flow and take the shape of their container as the particles can move quickly in all directions
- Gases can be compressed or squashed as particles are far apart and have space to move into
What are the changes in state between solid and liquid
solid to liquid = melting
liquid to solid = freezing
What are the changes in state between liquid and gas
liquid to gas = evaporation / boiling
gas to liquid = condensation
What are the changes in state between solid and gas
solid to gas = sublimation
gas to solid = deposition
How does pressure affect the states of matter?
If pressure is increased enough a gas will liquefy. This is because particles are moved close enough for bonds to be formed between the particles
How does temperature affect states of matter?
Energy, as heat, is added to break the bonds and to allow particles to move more freely. A change of state occurs when enough bonds are broken to allow a change in position and movement of particles.
What is the difference between evaporation and boiling?
In evaporation, the particles gain enough energy, they move apart, and form a gas. Bubbles do not form as vapour pressure is less than atmospheric pressure. In boiling there are still particles gaining energy, however, the vapour pressure is equal to the surrounding atmospheric pressure.
What is the kinetic theory of an ideal gas?
An attempt to explain the observable properties of gas
1. Gases are made of particles in constant random motion
2. The particles move very fast and collide with each other and the walls of their container with perfectly elastic collisions (they bounce but lose no energy)
3. The particles are negligible in size compared to the spaces in between them
4. There are no attractive or repulsive forces in between the particles
5. The average kinetic energy of the molecules is proportional to the temperature of the gas
No real gas shows all these properties. The gases with the smallest molecules e.g. hydrogen, helium approach ideal behaviour compared to heavier ones
What temperature is absolute zero, and what happens at this temperature?
-273°C or 0 K. When this temperature is reached, all particle motion stop. There is no temperature lower than absolute zero as particles cannot have negative motion.
What is gas pressure?
Gas pressure is the result of collisions of gas particles with the walls of the container. If the number of gaseous particles are doubled, the gas pressure is doubled
What are exceptions to kinetic theory of gases?
At high pressures, the gas particles are close together so the volume of the container will have to be reduced to produce the very high pressures. The intermolecular forces between the gas molecules are strong enough to affect the collisions of the molecules and pull them away from the walls of their container. This reduces the pressure exerted on the container’s wall.
Under very low temperatures, gas particles no longer have enough kinetic energy to overcome the attractive forces between them as the particles are moving very slowly.
Explain Brownian motion
Particles in both liquid and gases move randomly. They do this because they are bombarded by other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules.
What evidence is there for Brownian motion?
When smoke particles are viewed under a microscope they appear to ‘dance around’ when illuminated with a light beam at 90° to the viewing direction. This is because the smoke particles show up by reflected light and ‘dance’ due to millions of random hits from the fast moving air molecules. This is called ‘Brownian Motion’
What is diffusion?
Diffusion is the random movement of liquid and gas particles from regions of high concentration to regions of low concentration.
What are the three chemical factors that affect rates of diffusion?
- Molecular mass - Heavier particles diffuse more slowly while lighter particles move quicker.
- Temperature - the rate of diffusion increases with increase in temperature as the particles gain more kinetic energy and move faster.
- Concentration gradient - This is the difference between the two areas the liquid or gas molecules are diffusing down. The greater the difference, the faster the rate of diffusion.
Describe diffusion in gases compared to liquids
The natural rapid and random movement of the particles in all directions means that gases readily ‘spread’ or diffuse.
Diffusion of gases is faster than in liquids as there is more space for them to move into.
List most accurate apparatus for measuring volume from pipette, burette and measuring cylinder
Measuring cylinder, Pipettes, Burettes
Define a solute
A dissolved substance
Define a solvent
A substance which dissolves a solute
Define miscible liquids
Liquids that are completely soluble in each other
Define immiscible liquids
Liquids that are not soluble in each other
Define a solution
Mixture that appears to have one substance
Define a suspension
A mixture where two or more parts can be seen
Define an element
Something which contains atoms of the same type (all atoms have the same number of protons)
Define a compound
Something which has two or more types of atoms which are chemically bonded together
Define a mixture
A substance of two or more types of atoms that are not chemically bonded together
Define a molecule
Two or more atoms that are covalently bonded together
Explain filtration
Separates insoluble solids from a liquid. The mixture is poured through filter paper with tiny pores. The solid remains on the filter paper, while the liquid falls through
Explain Decanting
It is used to separate two immiscible liquids. The denser of the two liquids would move to the bottom, while the less dense liquid will remain on the top. You can then separate by either pouring the top liquid out, or you can use a separating funnel to tap out the denser liquid.
Explain Chromatography
Used to separate a mixture of substance into their components. The solutes are blotted onto a line drawn with pencil on a piece of chromatography paper. This is placed in a solvent such as water or ethanol. As the solvent rises up the paper, the substance separates out into individual components. Parts which are the most soluble move further up the paper, while least soluble move very little. Final distance is measured, called the solvent front. This is used to measure Rf value which is compared to a database which has Rf values for many substances.
Explain Evaporation
Is used to obtain a solute from a solvent. This is done by vaporising the liquid from the solid. Only the solid is obtained.
Explain Simple Distillation
Separating two liquids using their boiling points. Liquid with the lower boiling point evaporates first, rises and travels through a condenser where it is cooled using cold water. The gas condenses into a liquid which can be collected. Simple distillation can also be used to separate a dissolved solute from a solvent, and obtain the solvent.
Explain Fractional Distillation
Separating of two or more volatile liquids based on the differences in boiling points. Fractional distillation is the same as simple distillation however, it has a fractionating column filled with glass beads. This increases the surface area for molecules of varying fractions to condense to liquids and this means that the results are of greater purity.
Explain Diffusion (separation method)
Used to separate gases based on their diffusion rates. This is based on the idea that smaller molecules diffuse faster.
Explain Sublimation
Involves heating a mixture of two solids, one of which will sublime. The vapour is condensed leaving the two solids separated.
Explain Magnetism
Used to separate a magnetic and a non-magnetic substance. A magnet is used to attract the magnetic item, while the non-magnetic substance is left behind.
Explain Centrifugation
Used to separate a solid from a liquid when solid particles are so small they spread out in the liquid. The way it works is that a centrifuge spins the suspension very fast using the force of gravity to fling heavy particles to the bottom of the tube. An example is when separating blood.
Explain Crystallisation
To obtain pure solids from a saturated solution. This is done through placing the solution under strong heat so that it decomposes. Most of the solvent will evaporate and dissolved solid will appear as pure crystals. These crystals must be washed and dried to obtain optimal purity.
What can the melting point and boiling point tell us about a substance?
It can tell us the purity of a substance. If a substance is pure its melting/boiling point will match those in the data book. However, impurities cause the boiling/melting point to change
Define an atom
building blocks of matter; (proton/neutron), electron shell
Define an ion
Charged atom that has gained/lost electrons to have a full valence shell
Define a pure substance
A substance that contains only one type of particle
Name the subatomic particles in atoms
Protons, Neutrons, Electrons
What is the mass of electrons?
1/1840 amu (atomic mass units)
What is the proton number?
The number of protons in the nucleus of an atom
What is the atomic mass number?
The sum of protons and neutrons in the nucleus
What is an isotope?
Isotopes are two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties. Their varying number of neutrons may lead to radioactivity
Explain the two types of isotopes
Isotopes can be radioactive or non-radioactive. Certain elements have unstable isotopes. The nuclei of such atoms break up spontaneously and emit certain types of radiation. These isotopes are said to be radioactive and are called radioisotopes. They are said to decay or disintegrate. One or more of α-particles, β-particles and gamma radiation may be emitted. When a radioactive isotope emits gamma radiation, it loses energy and becomes unstable.
What is relative atomic mass?
Numbers used to compare the masses of atoms with accepted standard mass. It has no units.
What is the formula for relative atomic mass
sum of all (percentage abundance x mass numbers) / 100
What is the formula for the amount of element (in moles)
mass(g)/ Molar mass (g/mol)
What is the attraction between positive and negative ions called?
An electrostatic attraction.
What are features of ionic bonding
- High melting points
- Only conduct electricity in molten form or dissolved (not while solid)
- Brittle
- lattice shaped
What is a monotomic ion?
Are formed when one atom loses or gains electrons to form ions. E.g.H+, Ca 2+, O 2-, F-
List the main polyatomic ions
ammonium (NH4 +) nitrate (NO3 -)
carbonate (CO3 2-) sulfate (SO4 2-)
peroxide (O2 2-) hydrogen carbonate/
hydroxide (OH -) bicarbonate (HCO3 -)
thiosulfate (S2O3 2-) phosphate (PO4 3-)
ethanoate/ permanganate/
acetate (CH3COO -) manganate (MnO4 -)
carbide (C2 2-)
Define isoelectronic
When two atoms, ions or compounds have the same electron structure. E.g. O 2- and Mg 2+
Explain covalent bonding
Covalent bonding occurs between non-metal atoms. IN colvalent bonding electrons are shared.
Explain VSEPR theory
Valence shell electron pair repulsion theory. Electrons will repel each other until they reach maximum separation to minimise repulsion
State the five simple shapes of molecules
linear, bent, trigonal planar, trigonal pyramidal, tetrahedral
Explain the linear shape
This shape is formed when there are 2 electron clouds around the central atom. The angle is 180°
Explain the trigonal planar shape
This shape is formed when there are 3 electron clouds around a central atom. The angle is 120°
Explain the bent shape
This shape is formed with a varying number of electron domains and lone pairs. In sulfur dioxide, there are 3 electron clouds and one lone pair. In water there are 4 electron domains and 2 lone pairs.
Explain the tetrahedral shape
This shape is formed when there are 4 electron clouds around the central atom. The angle is 109.5°
Explain the trigonal pyramidal shape
This shape is formed when there are 3 electron pairs and one lone pair around the central atom
Define intermolecular bonding
Bonds that are formed between molecules.
Explain Van Der Waals forces
- Force of attraction that exist between all molecules and atoms.
- They are very weak inter-molecular bonds
- This is due to a temporary dipole in a molecule
- The more electrons there are, the stronger the temporary dipole
Explain dipole-dipole forces
- Also known as polar covalent bonds
- Some covalent bonds have uneven sharing of electron pairs as one of the atoms has a slightly stronger attraction. As a result, the shared pair of electrons are closer to the atom. This gives that atom a negative charge and the other, a positive charge.
Explain hydrogen bonds
They occur when hydrogen is bonded to an atom of oxygen, fluorine or nitrogen, forming polar bonds. Hydrogen bonds are a highly polar bond and therefore, their bonds are harder to break than polar covalent bonds or Van der Waals, however, they are still weaker than covalent bonds.
Explain metallic bonding
Metal atoms give up their outermost electrons to form positive ions. These electrons then surround the positive metal ions in a sea of delocalised electrons.
Define an alloy
A mixture of two elements, one of which is a metal. They usually have different properties to the metals which they contain.
Describe the arrangement of the periodic table
Elements are arranged in order of increasing atomic number. Groups are vertical columns numbered I= I to 0 (or alternatively 1 - 18). The rows are called periods
What are the five groups in the periodic table?
Alkali metals, Alkali Earth metals, Transition metals, Halogens, Noble (Inert) Gases
Describe the alkali metals
- Ion charge of 1+
-Found in nature as salts
-Very reactive, reactivity increases as you go down the group
-Low density solids, can cut with a spoon, density increases as you go down the group
-Basic (pH > 7) oxides
metal + water → metal hydroxide + hydrogen
Describe the alkali earth metals
- Ion charge of 2+
- Found as salts or deposits
- fairly reactive, reactivity increases as you go down the group
- higher density than alkali metals, density increases as you go down the group
- Basic oxides
- Metal hydroxides partially soluble
Describe the transition metals
- Variable charges of ions
- Found as ores
- reactivity varies, low reactivity, many catalysts
- high density solids
- some basic oxides, some are amphoteric (able to be base and acid)
- metal hydroxides are insoluble in water
Describe the halogens
- Ion charge of -1
- Found as diatomic molecules
- Fairly reactive, reactivity decreases down the group
- Fl, Cl (g)
- Br (l)
- I (s)
- Acidic oxides
- displacement reactions
Describe the noble gases
- Don’t form ions
- Monatomic gases
- unreactive
- low density gases
What are the colours of the halogens?
Fluorine = pale yellow gas , Aqueous = Pale yellow
Chlorine = pale green gas , Aqueous = Pale yellow
Bromine =orange-brown liquid, aqueous=orange-brown
Iodine = grey-black solid, aqueous = red-brown
What is an allotrope?
Same element, exists in different forms
Discuss diamond
- Tetrahedral and 3D
- Made from carbon
- All electrons are in bonds = non conductive
Discuss graphite
- Made from carbon
- 3 electrons in bond, One = delocalised
- Conducts electricity because of delocalised electron
- Van der Waals hold layers together making them weak and allowing them to slide off.
- Commercially made into diamond under extreme heat and pressure
Discuss Silicon Dioxide
- SiO2
- Similar structure to diamond
- No free electrons = no conductivity
- No layers
- Known as glass
Discuss Buckminster ‘Bucky balls’ Fullerene
- C60
- Spherical
- Three electrons bonded, one delocalised making it a conductor
- Soft powder
What is Avagadro’s number?
6.02 x 10^23
What is Avagadro’s hypothesis?
Equal volumes of all gases under the same conditions of temperature and pressure contain the same number of particles.
What is the formula for number of moles
n = Volume / 24
What is empirical formula?
Simplest whole number ratio of a compound
What is molecular formula?
Actual number of atoms in each element of a molecule
How to find the empirical formula?
- Assume 100g
- Find ‘n’
- Divide by smallest number of moles
- Ratio into formula
