Matter, bonding and structure
The particle model, atomic structure and electron configuration, and ionic, covalent and metallic bonding for G3 Pure and O-Level Chemistry.
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Before you begin
Everything is made of particles, and almost every property of a substance can be explained by what those particles are and how they are held together. The lessons start with the particle model of solids, liquids and gases, then look inside the atom at protons, neutrons and electrons. The arrangement of the electrons explains how atoms form ionic, covalent and metallic bonds, and the type of bonding and structure explains melting points, conductivity, hardness and the other properties of substances.
Be comfortable with: measurement and experimental techniques, especially temperature measurement and reading graphs.
Learning goals
- Describe solids, liquids and gases and explain changes of state using the kinetic particle theory and energy changes
- Describe and explain evidence that particles move in liquids and gases
- Explain everyday diffusion, such as spreading smells or tea and coffee in water, in terms of particles
- State how molecular mass affects the rate of diffusion and explain why diffusion is faster at higher temperature
- State the relative charges and approximate relative masses of protons, neutrons and electrons
- Describe and draw an atom as a nucleus of protons and neutrons with electrons in shells
- Define proton number (atomic number) and nucleon number (mass number)
- Read and write nuclide notation such as ¹²₆C
- Define isotopes
- Work out the numbers of protons, neutrons and electrons in atoms and ions from proton and nucleon numbers
- Describe how atoms lose or gain electrons to form ions, which usually have a noble-gas electronic configuration
- Describe ionic bonding between metals and non-metals, such as in NaCl and MgCl₂, using dot-and-cross diagrams
- State that an ionic compound is a giant lattice of ions held together by electrostatic attraction, such as NaCl
- Relate the physical properties of ionic compounds, including electrical conductivity, to their lattice structure
- Describe a covalent bond as a shared pair of electrons, with the bonded atoms usually reaching a noble-gas electronic configuration
- Draw dot-and-cross diagrams for covalent bonds between non-metals, such as in H₂, O₂, H₂O, CH₄ and CO₂
- Deduce the electron arrangement in other covalent molecules
- Relate the physical properties of covalent substances, including electrical conductivity, to their structure and bonding
- Describe a metal as a lattice of positive ions in a 'sea of electrons'
- Explain the high melting and boiling points, malleability and good conductivity of metals using their structure
- Describe how elements, compounds and mixtures differ
- Describe an alloy as a mixture of a metal with another element, such as brass or stainless steel
- Recognise metals and alloys in structure diagrams
- Explain why an alloy's physical properties differ from those of its constituent elements
- Deduce the properties of simple molecular substances, such as methane and iodine, from their structure
- Deduce the properties of macromolecules, such as poly(ethene), from their structure
- Deduce the properties of giant covalent substances, such as silicon dioxide, diamond and graphite, from their structure
- Compare the bonding and structures of diamond and graphite to deduce properties such as conductivity, lubrication and cutting action
- Deduce a substance's physical and chemical properties from its structure and bonding, and the reverse
Syllabus statements covered
- describe the solid, liquid and gaseous states of matter and explain their interconversion in terms of the kinetic particle theory and of the energy changes involved
- describe and explain evidence for the movement of particles in liquids and gases (the treatment of Brownian motion is not required)
- explain everyday effects of diffusion in terms of particles, e.g. the spread of perfumes and cooking aromas; tea and coffee grains in water
- state qualitatively the effect of molecular mass on the rate of diffusion and explain the dependence of rate of diffusion on temperature.
- state the relative charges and approximate relative masses of a proton, a neutron and an electron
- describe, with the aid of diagrams, the structure of an atom as consisting of protons and neutrons (nucleons) in the nucleus and electrons arranged in shells (energy levels) (knowledge of s, p, d and f classification is not required; a copy of the Periodic Table will be available in Papers 1 and 2)
- define proton (atomic) number and nucleon (mass) number
- interpret and use nuclide notations such as ¹²₆C
- define the term isotopes
- deduce the numbers of protons, neutrons and electrons in atoms and ions given proton and nucleon numbers.
- describe the formation of ions by electron loss/gain and that these ions usually have the electronic configuration of a noble gas
- describe, including the use of ‘dot-and-cross’ diagrams, the formation of ionic bonds between metals and non-metals, e.g. NaCl; MgCl2
- state that ionic materials contain a giant lattice in which the ions are held by electrostatic attraction, e.g. NaCl (candidates will not be required to draw diagrams of ionic lattices)
- relate the physical properties (including electrical property) of ionic compounds to their lattice structure (see also 3.4(g)).
- describe the formation of a covalent bond by the sharing of a pair of electrons and that the atoms in the molecules usually have the electronic configuration of a noble gas
- describe, using ‘dot-and-cross’ diagrams, the formation of covalent bonds between non-metallic elements, e.g. H2; O2; H2O; CH4; CO2
- deduce the arrangement of electrons in other covalent molecules
- relate the physical properties (including electrical property) of covalent substances to their structure and bonding (see also 3.4(g)).
- describe metals as a lattice of positive ions in a ‘sea of electrons’
- describe the general physical properties of metals as solids having high melting and boiling points, malleable, good conductors of heat and electricity in terms of their structure (see also 3.4(g)).
- describe the differences between elements, compounds and mixtures
- describe an alloy as a mixture of a metal with another element, e.g. brass; stainless steel
- identify representations of metals and alloys from diagrams of structures
- explain why alloys have different physical properties to their constituent elements
- compare the structures of the following substances in order to deduce their properties: — simple molecular substances, e.g. methane, iodine
- compare the structures of the following substances in order to deduce their properties: — macromolecules, e.g. poly(ethene)
- compare the structures of the following substances in order to deduce their properties: — giant covalent substances, e.g. sand (silicon dioxide), diamond, graphite (see also 3.4(g))
- compare the bonding and structures of diamond and graphite in order to deduce their properties such as electrical conductivity, lubricating or cutting action (candidates will not be required to draw the structures)
- deduce the physical and chemical properties of substances from their structures and bonding and vice versa (see also 3.1(d), 3.2(d), 3.3(b) and 3.4(e)).
Lessons
Work through them in order.
Particle model
- What is matter?What counts as matter, the difference between atoms, molecules and ions, and how solids, liquids and gases compare.
- Kinetic particle theoryUse moving particles to explain the properties of solids, liquids and gases, temperature and gas pressure.
- Changes of state and heating curvesExplain each change of state with particles and energy, and read heating and cooling curves.
- DiffusionExplain diffusion from random particle motion, and how state, temperature and molecular mass change its rate.
Atoms and ions
- Atomic structure and particle countsDescribe the particles in an atom and count the protons, neutrons and electrons in atoms and ions.
- Elements and isotopesWhat makes atoms the same element, what isotopes are, and why relative atomic masses are not whole numbers.
- Electron configurationWrite electron configurations for the first 20 elements and use them to find group and period.
Composition, bonding and structure
- Elements, compounds and mixturesTell elements, compounds and mixtures apart, and explain why an alloy is a mixture.
- Ionic bonding: forming ions and balancing chargesExplain how metals and non-metals form ions, draw dot-and-cross diagrams and write formulas from ion charges.
- Ionic structures and propertiesUse the giant ionic lattice to explain high melting points and when ionic compounds conduct.
- Covalent bonding and electron diagramsExplain covalent bonds as shared electron pairs and draw dot-and-cross diagrams with single, double and triple bonds.
- Molecular structures and propertiesExplain why simple molecular substances have low melting points and do not conduct.
- Metallic bonding and metal propertiesExplain the conductivity, high melting points and malleability of metals from positive ions in a sea of electrons.
- Why alloys have different propertiesIdentify alloys in particle diagrams and explain why they are harder than pure metals.
- Giant covalent structures: diamond, graphite and silicaExplain the hardness, conductivity and high melting points of diamond, graphite and silicon dioxide.
- Comparing covalent structuresCompare simple molecules, poly(ethene) and giant covalent structures, and deduce structure from properties.
Practise and check
Or choose
Topic reference
Quick reference
| Item | Quick rule / reminder |
|---|---|
| Changes of state | melting, boiling and sublimation absorb energy; freezing and condensation release it |
| Heating curve | flat sections at the melting and boiling points; energy overcomes attractions instead of raising temperature |
| Diffusion rate | faster in gases than liquids; faster at higher temperature; faster for lower Mᵣ |
| Subatomic particles | proton: mass 1, charge +1; neutron: mass 1, charge 0; electron: mass 1/1840, charge −1 |
| Nuclide notation | X with nucleon number A and proton number Z: protons = Z; neutrons = A-Z; electrons = Z in a neutral atom |
| Shells (first 20) | 2, 8, 8, 2 |
| Group and period | period = number of occupied shells; Groups 1–2 = outer electrons; Groups 13–17 = outer electrons + 10 |
| Ionic bonding | metal loses electrons, non-metal gains them; oppositely charged ions attract |
| Covalent bonding | non-metal atoms share pairs of electrons |
| Metallic bonding | positive ions attracted to a sea of delocalised electrons |
| Ionic compounds | high melting points; conduct only when molten or dissolved |
| Simple molecular | low melting points; do not conduct |
| Giant covalent | very high melting points; only graphite conducts |
| Metals | high melting points; conduct as solids; malleable and ductile |
Core knowledge to remember
- Matter: anything that has mass and occupies space.
- Diffusion: the net movement of particles from a region of higher concentration to a region of lower concentration, caused by their random motion.
- Proton number: the number of protons in the nucleus of an atom. Nucleon number: the total number of protons and neutrons.
- Isotopes: atoms of the same element with the same number of protons but different numbers of neutrons.
- Element: a substance made of only one kind of atom. Compound: two or more elements chemically combined in a fixed ratio. Mixture: substances not chemically combined.
- Alloy: a mixture of a metal with one or more other elements.
- Ionic bond: the strong electrostatic attraction between oppositely charged ions.
- Covalent bond: a shared pair of electrons between two atoms.
- Metallic bond: the strong electrostatic attraction between positive metal ions and a sea of delocalised electrons.
- Giant covalent structure: a network of atoms joined by covalent bonds throughout, with no separate molecules.
Common mistakes
- Diffusion: particles move randomly in all directions; only the net movement is from high to low concentration.
- Changes of state: the temperature of a pure substance stays constant while it melts or boils.
- Ions: forming an ion changes the number of electrons, never the number of protons.
- Isotopes: they have different numbers of neutrons but very similar chemical properties.
- Ionic bond: the bond is the attraction between the ions, not the transfer of electrons.
- Simple molecules: melting and boiling overcome weak forces between molecules; the covalent bonds inside them do not break.
- Ionic conductivity: solid ionic compounds do not conduct, because their ions cannot move.
- Graphite: it is soft because its layers slide, and conducts because of delocalised electrons; its covalent bonds are strong.
- Alloys: they are mixtures, and they are harder because different-sized atoms stop the layers sliding.