november mocks

what is a hazard

something that could cause harm to someone, damage to something or adverse health effects either straightaway or later

example of a hazard

concentrated acids are corrosive, this is a hazard as acids can damage skin and clothes if they are split

using hazard symbols

hazard symbols are used on containers, they are there to: indicate the dangers associated with the substance inside and give information about how to work safely with the substance in the laboratory

using hazard symbols

meaning moderate health hazard, typically causes skin irritation

using hazard symbols

meaning serious health hazard, typically causes breathing difficulties

using hazard symbols

meaning toxic, typically could cause death if swallowed or inhaled

using hazard symbols

meaning corrosive, typically damages skin and clothing

using hazard symbols

meaning flammable, typically catches fire easily

using hazard symbols

meaning oxidising, typically makes flammable substances burn more fiercely

using hazard symbols

meaning harmful to the environment, typically could cause damage to animal and plant life

what is a risk

a risk is the chance that a hazard will cause harm

factors to think about when evaluating a risk

the way the hazard causes harm, how likely it is that someone or something will be exposed to the hazard and how serious the effects of the hazard could be

precaution

something that can be done to reduce a risk of harm, different substances and different practical procedures need different precaution

risk assessment

describes the hazards and risks of harm, and what suitable precautions are needed to work more safely

examples of precautions

using less hazardous substances, wearing eye protection, protective gloves or other protective clothing and choosing different apparatus or a different method

what must be done when suggesting suitable precautions

make sure the suggestions are appropriate to the particular procedure. e.g, the risk of harm from hydrochloric acid is reduced if the acid is diluted with water, and if eye protection and gloves are worn

John Dalton

John Dalton published his ideas about atoms in 1803, he thought that all matter was made of tiny particles called atoms, which he imagined as tiny solid balls

the ideas of the Dalton model

atoms cannot be broken down into anything simpler, the atoms of a given element are identical to each other, the atoms of different elements are different from one another and during chemical reactions atoms rearrange to make different substances

a timeline of discovery for developing models of atoms

1897: electrons, 1909 - 1911: atoms have a nucleus with electrons around it,1913: electrons occupy shells (energy levels), 1918: protons, 1932: neutrons

what do we understand as a result of the timeline of discovery for developing models of atoms

atoms can be broken down into three smaller particles: protons, neutrons and electrons, atoms of an element have identical numbers of protons and electrons, but can have different numbers of neutrons and atoms of different elements have different numbers of protons and electrons

atom

has a central nucleus surrounded by electrons arranged in areas called shells

compare the nucleus to the atom

as electrons are even smaller, most of an atom is empty space and the diameter of a nucleus can be 100,000 times less than the diameter of an atom

nuclei of an atom

the nuclei of all atoms contain subatomic particles called protons and most also contain neutrons

protons

relative mass = 1, relative charge = +1

neutrons

relative mass = 1, relative charge = 0

electrons

relative mass = 1/1835, relative charge = -1

atomic number

the number of protons in its nucleus, all the atoms of a given element have the same atomic number and the atomic number of each element is unique - no two elements have the same atomic number

number of protons an electrons in an atom

an atom contains equal numbers of protons and electrons, since protons and electrons have equal and opposite charges, this means that atoms are neutral overall

mass number of an atom

the total number of protons and neutrons in its nucleus

how to calculate the number of protons?

atomic number

how to calculate the number of neutrons?

mass number - atomic number

how to calculate the number of electrons?

atomic number

isotopes

atoms of an element with the same number of protons and electrons but different number of neutrons

features of Mendeleev’s tables

Mendeleev arranged the elements in order of increasing relative atomic mass, when he did this he noted that the chemical properties of the elements and their compounds showed a periodic trend, he then arranged the elements by putting those with similar properties below each other into groups

what changes did Mendeleev make to make his classification work?

he left gaps for yet to be discovered elements and he switched the order of a few elements to keep the groups consistent

what changes did Mendeleev make to make his classification work?: prediction using gaps (1)

Mendeleev left gaps in his table to place elements not known at the time. by looking at the chemical properties and physical properties of the elements next to a gap, he could also predict the properties of these undiscovered elements

what changes did Mendeleev make to make his classification work?: prediction using gaps (2) examples

e.g, Mendeleev predicted the existence of 'eka-silicon', which would fit into a gap next to silicon, the element germanium was discovered later, its properties were found to be similar to the predicted ones and confirmed Mendeleev's periodic table

what changes did Mendeleev make to make his classification work?: pair reversals

Iodine has a lower relative atomic mass than tellurium, so iodine should be placed before tellurium in Mendeleev's tables, however, iodine has similar chemical properties to chlorine and bromine, to make iodine line up with chlorine and bromine in his table, Mendeleev swapped the positions of iodine and tellurium

how are elements arranged in the modern periodic table

according to their atomic number, in the periodic table the elements are arranged into: rows, called periods, in order of increasing atomic number and vertical columns, called groups, where the elements have similar properties

metals and non metals in the table

the metal elements are found on the left hand side of the periodic table, and the non-metal elements are found on the right

resolving pair reversals (1)

Mendeleev did not know about isotopes, but their existence is an explanation for pair reversals in his table, the positions of iodine and tellurium were reversed in Mendeleev's table because: iodine has one naturally occurring isotope, iodine-127 and the most abundant tellurium isotopes are tellurium-128 and tellurium-130

electronic configuration

the way in which electrons are arranged in an atom

how is the electronic configuration of an element related to its position on the periodic table (1)

the number of circles in the electronic configuration of an element is represented in the periodic table as the period number that element is situated in

how is the electronic configuration of an element related to its position on the periodic table (2)

the number of electrons in the outermost shell of an element is represented in the periodic table as the group number that element is situated in

how is the electronic configuration of an element related to its position on the periodic table (3)

the number of electrons in all shells of an element is represented in the periodic table as the element's atomic number

how does the electronic configurations of atoms explain the properties of elements and the structure of the periodic table? (1)

when atoms collide and react, it is the outer electrons that meet and interact, so, elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell

how does the electronic configurations of atoms explain the properties of elements and the structure of the periodic table? (2)

the atoms of all group 1 elements have similar chemical properties and reactions because they all have one electron in their outer shell

what is an ion

an atom or group of atoms with a positive or negative charge. Ions form when atoms lose or gain electrons to obtain a full outer shell: metal atoms lose electrons to form positively charged ions and non-metal atoms gain electrons to form negatively charged ions

forming positive ions

metal atoms lose electrons from their outer shell when they form ions: the ions formed are positive, with more protons than electrons and the ions formed have full outer shells

forming negative ions

the outer shell of non-metal atoms gains electrons when they form ions: the ions formed are negative, because they have more electrons than protons and the ions formed have full outer shells

cations and ions

positively charged ions are called cations, and negatively charged ions are called anions, these ions can form when a metal reacts with a non-metal, by transferring electrons, the oppositely charged ions are strongly attracted to each other, forming ionic bonds

dot and cross diagrams

can model the transfer of electrons from metal atoms to non-metal atoms, the electrons from one atom are shown as dots, and the electrons from the other atom are shown as crosses

regular arrangement of ions in an ionic lattice

the ions in a solid ionic compound are not randomly arranged. Instead, they have a regular, repeating arrangement called an ionic lattice, the lattice is formed because the ions attract each other and form a regular pattern with oppositely charged ions next to each other

ionic bonds

the ionic lattice is held together by ionic bonds, in three-dimensional models, ionic bonds are shown as straight lines between ions, this is to keep things simple because ionic bonds can act in any direction, ionic bonds are strong electrostatic forces between oppositely charged ions

physical properties of ionic compound: high melting and boiling points (1)

ionic compounds are solids at room temperature, melting and boiling are state changes, energy has to be transferred to a substance in order to melt or boil it, this energy is needed to break the bonds between particles in the substance

physical properties of ionic compound: high melting and boiling points (2)

some bonds are overcome during melting, all remaining bonds are overcome during boiling, the more energy needed, the higher the melting point or boiling point

explain high melting and boiling points in ionic compounds

ionic compounds are held together by many strong electrostatic forces between the oppositely charged ions, these forces are usually referred to as ionic bonds, as the ionic lattice contains such a large number of ions, a lot of energy is needed to overcome these ionic bonds so ionic compounds have high melting and boiling points

physical properties of ionic compounds: conduction of electricity

a substance can conduct electricity if: it contains charged particles, and these particles are free to move from place to place

explain conduction of electricity in ionic compounds

ionic compounds conduct electricity when molten to form a liquid or dissolved in water to form an aqueous solution as both processes make their ions free to move from place to place, ionic compounds cannot conduct electricity when solid, as their ions are held in fixed positions and cannot move

polyatomic ions (cations)

ammonium (NH₄⁺), calcium (Ca²⁺), sodium (Na⁺), lead (Pb²⁺)

polyatomic ions (anions)

hydroxide (OH⁻), nitrate (NO₃⁻), carbonate (CO₃²⁻), sulfate (SO₄²⁻)

naming ionic compounds with ide and ate

the name of an ionic compound ends in: -ide if it contains just two elements and -ate if it contains three or more elements, one of which is oxygen

covalent bonds

a covalent bond is formed when a pair of electrons is shared between two atoms, usually non-metals, these shared electrons are found in the outer shells of the atoms. In general, each atom contributes one electron to the shared pair of electrons

molecules

consists of a group of two or more atoms joined together by covalent bonds, molecules of the same element or compound will have a set size - in other words, they will always contain the same number of atoms of each element

typical size of a molecule

0.1nm, individual atoms and molecules are too small to see even with the strongest light microscope, some electron microscopes can produce images of atoms and simple molecules

how are dot and cross diagrams drawn

a dot and cross diagram can model the bonding in a simple molecule: the outer shell of each atom is drawn as a circle, circles overlap where there is a covalent bond and electrons from one atom are drawn as dots, and electrons from another atom as crosses

how are molecular drawings drawn

a simple molecule can be modelled by drawing its structure, in these structures: show each atom by its element symbol and show each covalent bond as a straight line

properties of simple molecular substances: low melting and boiling points

simple molecular substances generally have low melting points and boiling points and are often liquids or gases at room temperature.

explain low melting and boiling points in simple molecular substances (1)

there are intermolecular forces between simple molecules, these intermolecular forces are much weaker than the strong covalent bonds in molecules, when simple molecular substances melt or boil, it is these weak intermolecular forces that are overcome

explain low melting and boiling points in simple molecular substances (2)

the covalent bonds are not broken, very little energy is needed to overcome the intermolecular forces, so simple molecular substances usually have low melting and boiling points

properties of simple molecular substances: conduction of electricity (1)

a substance can conduct electricity if: it contains charged particles, and these particles are free to move from place to place

properties of simple molecular substances: conduction of electricity (2)

simple molecules have no overall charge, or charged particles that can separate, so simple molecular substances cannot conduct electricity, even when liquid or dissolved in water.

substances with many covalent bonds

covalent bonding leads to the formation of molecules, these can be: simple molecules, which contain a set number of atoms joined by covalent bonds or giant covalent substances, which contain many atoms joined by covalent bonds

substances with many covalent bonds: silica (example) (1)

silica is the main compound found in sand. It is an example of a giant covalent substance, it contains many silicon and oxygen atoms, these are joined together by covalent bonds in a regular arrangement, forming a giant covalent network or lattice structure

substances with many covalent bonds: silica (example) (2)

there is no set number of atoms joined together in this type of structure, so these covalent lattices are not classed as molecules, however, the atoms in the compound will be present in the ratio indicated by the chemical formula

substances with many covalent bonds: high melting point and boiling point

giant covalent substances are solids at room temperature and have very high melting points and boiling points, covalent bonds are strong, so a lot of energy is needed to break up these large structures during melting and boiling

substances with many covalent bonds: conduction of electricity

giant covalent substances have no overall charge, so most cannot conduct electricity, graphite, a form of carbon, which can conduct electricity, is an exception

substances with many covalent bonds: insoluble in water

a substance can dissolve in water if it forms strong enough attractions with water molecules, giant covalent substances cannot form these strong attractions with water, so they are insoluble.

structure and bonding in diamond

diamond is a giant covalent substance in which: each carbon atom is joined to four other carbon atoms by covalent bonds, the carbon atoms form a regular tetrahedral network structure and there are no free electrons

properties and uses in diamond

the rigid network of carbon atoms, held together by strong covalent bonds, makes diamond very hard. This makes it useful for cutting tools, such as diamond-tipped glass cutters and oil rig drills.

structure and bonding in graphite

graphite is a giant covalent substance in which: each carbon atom is joined to three other carbon atoms by covalent bonds, the carbon atoms form a hexagonal layered network structure, the layers have weak forces between them and can slide over each other, each carbon atom has one un-bonded outer electron, these un-bonded electrons are delocalised, and are free to move

properties and uses of graphite

delocalised electrons are free to move through the structure of graphite, so graphite can conduct electricity, this makes it useful for electrodes in batteries and for electrolysis, the layers in graphite can slide over each other because the forces between them are weak, this makes graphite slippery, so it is useful as a lubricant

graphene

another form of carbon. Its structure resembles a single layer of graphite, very high melting point and is very strong because of its large regular arrangement of carbon atoms joined by covalent bonds, conducts electricity well because it has delocalised electrons that are free to move across its surface

what is a fullerene

molecular form of the element carbon

fullerenes (nanotubes)

a nanotube resembles a layer of graphene, rolled into a tube shape, nanotubes have high tensile strength, so they are strong in tension and resist being stretched, like graphene, nanotubes are strong and conduct electricity because they have delocalised electrons

fullerenes (buckyballs)

buckyballs are spheres or squashed spheres of carbon atoms, they are made up of large molecules so are not classed as giant covalent network, weak intermolecular forces exist between buckyballs, these need little energy to overcome, so substances consisting of buckyballs are slippery and have lower melting points than graphite or diamond

fullerenes (polymers)

simple polymers consist of large molecules that contain chains of carbon atoms of no set size, polythene molecules will contain thousands of carbon atoms joined together in a chain

physical properties of metals

shiny, high melting points, good conductors of electricity, good conductors of heat, high density and malleable

physical properties of non metals

dull, low melting points, poor conductors of electricity, poor conductors of heat, low density and brittle

atypical properties of metals and non metals

mercury (a metal) has a low melting point and exists as a liquid at room temperature and graphite, a form of carbon (a non-metal), has a high boiling point and is also a good conductor of electricity

high density

a substance with a high density means it has a high mass for its size

compare malleable and brittle substances

malleable substances can be bent or hammered into shape without shattering, while brittle substances shatter when bent or hit

ductile

means that a substance can be drawn out into a long wire without snapping or breaking

metallic structure and bonding

in metals, the electrons leave the outer shells of metal atoms, forming positive metal ions and a 'sea' of delocalised electrons, the structure of a solid metal consists of closely packed metal ions, arranged in a regular way to form a metallic lattice structure

what is metallic bonding

the strong electrostatic force of attraction between the metal ions and the delocalised electrons

explaining metal properties: malleability

metals are malleable because layers of ions can slide over each other when a force is applied, metallic bonding allows the metal to change shape without shattering

explaining metal properties: malleability

when a voltage is applied to a metal, the delocalised electrons travel through the lattice structure, the movement of these charged particles forms an electric current

kinetic particle theory of matter

the kinetic particle theory of matter is a model that describes the arrangement, movement and energy of particles in a substance, the model is used to explain the physical properties of solids, liquids and gases

particle arrangement and movement of solids

particles are very close together, particles are arranged in a regular pattern, particles move and vibrate in a fixed position, particles have low energy

particle arrangement and movement of liquids

particles are close together, particles are randomly arranged, particles move around eachother, particles have greater energy