2.3The Particulate Nature of Matter
Atomic structure and the Periodic Table — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
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Lesson summary
2.3 Atomic structure and the Periodic Table — COMBINED SCIENCE (CHEMISTRY) notes: Describe the structure of the atom, the particle numbers, electronic configuration and the link to the Periodic Table.Nucleus — the centre of the atom, containing protons and neutrons.Electrons — mo…
- Proton (atomic) number
- Mass (nucleon) number
- Outer shell
- Beyond argon
- Group VIII
- Proton number
Section 1 of 15Structure of the atom
Structure of the atom
Nucleus
- Nucleus the centre of the atom, containing protons and neutrons.
Electrons
- Electrons move very fast around the nucleus in shells.
Mass
- Mass the mass of an electron is negligible, so almost all the mass is in the nucleus.
Section 2 of 15Subatomic particles
| Particle | Relative mass | Relative charge | Location |
|---|---|---|---|
| Proton | 1 | +1 | Nucleus |
| Neutron | 1 | 0 | Nucleus |
| Electron | 1/1840 (negligible) | −1 | Shells outside nucleus |
Section 3 of 15Proton number and mass number
Proton (atomic) number
- = number of protons in the nucleus.
- It equals the number of electrons in a neutral atom.
- It decides which element the atom is.
Mass (nucleon) number
- = total number of protons and neutrons in the nucleus.
Neutrons
- Neutrons number of neutrons = mass number − proton number.
Section 4 of 15Electron shells
Filling
- Filling electrons fill the shell nearest the nucleus first.
- The first shell holds 2 electrons.
- The second and third shells each hold 8 in this model.
Outer shell
- Outer shell the outermost shell is the valence shell, and a full outer shell makes an atom stable.
Section 5 of 15Writing electronic configuration
Notation
- Notation write the number of electrons in each shell, separated by commas.
- Carbon is 2,4.
- Sodium is 2,8,1.
- Magnesium is 2,8,2.
- Argon is 2,8,8.
- Calcium is 2,8,8,2.
Beyond argon
- Beyond argon potassium and calcium put their extra electrons in the fourth shell.
Section 6 of 15Electronic configuration and the Periodic Table
Electronic configuration and the Periodic Table
Period
- Period the number of occupied shells equals the period number.
Group
- Group the number of outer electrons equals the group number for Groups I to VII.
Group VIII
- Group VIII the noble gases have a full outer shell.
Chlorine
- 2,8,7 has three shells and seven outer electrons, so it is in Period 3 and Group VII.
Section 7 of 15More from the specification
More from the specification
Chemical symbol
- A standard international one- or two-letter notation representing a specific chemical element.
- (e.g. H for hydrogen, Li for lithium)
Atoms and elements
- Fundamental building blocks of matter containing identical proton counts that cannot be chemically subdivided.
Chemical compounds vs mixtures
- Compounds consist of different elements chemically combined in fixed stoichiometric ratios, whereas mixtures retain separate physical identities.
Isotope abundance
- Relative natural proportions of different isotopes used to calculate accurate relative atomic masses.
Isotopes
- Atoms of the same element with the same number of protons but different numbers of neutrons.
Isotope
- Atoms of an element with different numbers of neutrons.
Hydrogen
- A gas that gives a squeaky pop with a lighted splint.
Compound
- Two or more elements chemically combined in a fixed ratio.
Mixture
- Two or more substances mixed but not chemically combined.
Symbol
- Shorthand for an element, e.g. Na.
Substance
- A material with only one type of particle.
Section 8 of 15Stable electronic structures
Stable electronic structures
Noble gases
- Noble gases have a full outer shell and are very unreactive.
Other atoms
- Other atoms gain, lose or share electrons to reach a full outer shell.
- Some atoms lose all outer electrons so that the shell below becomes a full outer shell.
Section 9 of 15Definition of isotopes
Isotopes
- = different atoms of the same element with the same number of protons but different numbers of neutrons.
Notation
- Notation the symbol or name is followed by the mass number, such as C-14 or carbon-14.
- It can also be written 14C.
Carbon-14
- Carbon-14 has 6 protons, 6 electrons and 14 − 6 = 8 neutrons.
Section 10 of 15Isotopes of hydrogen
| Isotope | Protons | Neutrons | Electrons |
|---|---|---|---|
| Hydrogen-1 | 1 | 0 | 1 |
| Hydrogen-2 | 1 | 1 | 1 |
| Hydrogen-3 | 1 | 2 | 1 |
Section 11 of 15Properties of isotopes
Chemical properties
- Chemical properties are the same because the isotopes have the same number of electrons and outer shell.
Physical properties
- Physical properties density, melting point and boiling point differ because the extra neutrons add mass but no charge.
Appearance
- Appearance isotopes of an element look identical.
Section 12 of 15Relative atomic mass
Relative atomic mass
Relative atomic mass, Ar
- = average mass of the isotopes of an element compared with 1/12 of the mass of a carbon-12 atom.
- It has no units.
Calculation
- Ar = sum of ÷ 100.
- (percentage of isotope × mass number)
Difference from mass number
- Difference from mass number relative atomic mass takes isotopes into account, so it is often not a whole number.
- Lithium is 6.94, shown as 7 on a table rounded to whole numbers.
Section 13 of 15More from the specification
More from the specification
Subatomic particles and the nucleus
- An atom consists of a dense central nucleus containing positively charged protons and neutral neutrons, surrounded by negatively charged electrons orbiting in energy shells.
Electronic configuration and the Periodic Table
- The electronic configuration dictates an element's position in the Periodic Table; the number of occupied shells corresponds to the period,
- (e.g. 2,8,7 for chlorine)
- while valence electrons determine the group.
Pure compounds vs mixtures
- Chemical compounds consist of two or more elements chemically combined in fixed ratios with properties distinct from constituent elements,
- whereas mixtures contain unbonded substances that retain their original properties.
Group properties in the Periodic Table
- Elements in the same vertical group possess identical valence electron configurations, exhibiting similar chemical reactivity and forming predictable ionic or covalent compounds.
Subatomic particles and the nucleus
- An atom consists of a dense central nucleus containing positively charged protons and neutral neutrons, surrounded by negatively charged electrons orbiting in energy shells.
Electronic configuration and the Periodic Table
- The electronic configuration dictates an element's position in the Periodic Table; the number of occupied shells corresponds to the period,
- (e.g. 2,8,7 for chlorine)
- while valence electrons determine the group.
Pure compounds vs mixtures
- Chemical compounds consist of two or more elements chemically combined in fixed ratios with properties distinct from constituent elements,
- whereas mixtures contain unbonded substances that retain their original properties.
Group properties in the Periodic Table
- Elements in the same vertical group possess identical valence electron configurations, exhibiting similar chemical reactivity and forming predictable ionic or covalent compounds.
Nucleus
- Central part of an atom with protons and neutrons.
Compound
- Two or more elements chemically combined in a fixed ratio.
Mixture
- Two or more substances mixed but not chemically combined.
Particle
- A tiny portion of matter, too small to see.
Substance
- A material with only one type of particle.
Electronic configuration
- The number of electrons in each shell, written with commas.
Section 14 of 15Key terms
| Term | Meaning |
|---|---|
| Nucleus | Centre of the atom containing protons and neutrons. |
| Proton number | Number of protons in the nucleus. |
| Mass number | Total number of protons and neutrons. |
| Electronic configuration | Number of electrons in each shell. |
| Valence shell | Outermost electron shell. |
| Noble gas | Group VIII element with a full outer shell. |
| Term | Meaning |
|---|---|
| Isotope | Atom of the same element with a different number of neutrons. |
| Relative atomic mass | Average mass of an element's atoms compared with 1/12 carbon-12. |
| Nucleon | A proton or a neutron. |
| Noble gas | Element with a full outer shell. |
| Neutron | Neutral particle in the nucleus. |
| Valency electron | Electron in the outer shell. |
Section 15 of 15Exam technique
1
Saying the mass number is the number of protons — it is protons plus neutrons.
2
Saying electrons have a mass of 1 — their mass is negligible.
3
Putting more than 2 electrons in the first shell.
4
Thinking the number of shells gives the group — it gives the period.
1
Saying isotopes have different numbers of protons — they differ in neutrons.
2
Saying isotopes have different chemical properties — they react the same way.
3
Saying relative atomic mass equals mass number — it is a weighted average.
4
Giving relative atomic mass units.
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