The History and Structure of the Atom

atom

the basic unit of a chemical element

atomic theory

the theory that all matter is made up of atoms

John Dalton

the scientist who developed atomic theory in 1810

Democritus

the Greek philosopher who proposed the existence of atoms around 450 BCE

Antoine Lavoisier

the French chemist who measured the composition of chemical compounds in the 1780s

fixed air

the former name for carbon dioxide, discovered to be heavier than air

ratio of oxygen to carbon in fixed air

the mass of oxygen in fixed air was always 2.66 times the mass of carbon

law of simple multiple proportions

the principle that elements combine in simple ratios, such as 2:1 in water (H2O)

formulas

the ratios in which elements combine, such as 2:1, 1:4, or 2:3

weight of atoms

Dalton assigned weights to atoms compared to the lightest atom, hydrogen

chemical analysis

the method used by chemists to determine the composition of compounds like ammonia (NH3), water (H2O), and carbon dioxide (CO2)

testable predictions

predictions made by a scientific theory that can be tested against evidence

elements

substances that can join together to form compounds

water composition

water always contains twice as much hydrogen as oxygen

mass conservation

the total mass of chemicals does not change when they react with each other

properties of pure oxygen

pure oxygen has the same properties wherever it is found on Earth or in space

mass of gases

gases have mass, and different gases have different masses

scanning tunnelling microscopes

modern instruments that produce images of surfaces that look 'bumpy'

pollen movement in water

tiny particles of pollen in water move in strange ways as if bumping into invisible objects

Oxygen molecule

An oxygen molecule is made up of two oxygen atoms.

Methane

Methane is formed from one carbon atom and four hydrogen atoms.

Water molecule

A water molecule is made up of one oxygen atom and two hydrogen atoms.

Carbon dioxide

Carbon dioxide is a compound made up of one carbon atom and two oxygen atoms.

Dalton's atomic model

Dalton's atomic model gave 'a physical explanation for reactions that could be expressed in quantitative terms'.

Democritus

A philosopher who proposed early ideas about atoms.

John Dalton

A scientist who developed atomic theory and was convinced atoms really existed.

Carbon dioxide formula

The formula of carbon dioxide is CO2.

Ammonia formula

The formula of ammonia is NH3.

Methane formula

The formula of methane is CH4.

Water formula

The formula of water is H2O.

Subatomic particles

Atoms are made of a nucleus, protons, neutrons, and electrons.

Rutherford model of the atom

The Rutherford model suggests that an atom has a central nucleus containing positively charged protons and neutrons with no charge.

Electron

An electron is a negatively charged subatomic particle that moves in the space around an atomic nucleus.

Gold foil experiment

An experiment that showed most alpha particles passed straight through gold foil, indicating atoms contain a lot of space.

Alpha particles

Alpha particles are radioactive particles that were used in Rutherford's gold foil experiment.

Nucleus of the atom

The nucleus of the atom contains a relatively large amount of positive charge.

Thomson's plum pudding model

An early model of the atom proposed by Thomson.

Scientific evidence

Evidence that can be used to support the existence of atoms.

Marie Curie

A physicist and chemist who faced prejudices as a woman in scientific research and continued her work after her husband's death.

Quantitative terms

Reactions that can be expressed in measurable quantities.

Radioactive particles

Particles that emit radiation, used in experiments to study atomic structure.

Experimental confirmation

The process of verifying scientific hypotheses through experiments.

Space outside the nucleus

Negatively charged electrons travel around the space outside the atom's nucleus.

Thomson plum pudding model

An early model of an atom that suggested that the positively charged nucleus had negatively charged electrons scattered through it (like a plum pudding).

Nucleus

The centre of an atom that contains protons (positive) and neutrons (no charge).

Proton

A positively charged subatomic particle in the nucleus of an atom.

Neutron

A neutral (no charge) subatomic particle in the nucleus of an atom.

Electrons

Negatively charged particles that move around in the space outside the nucleus.

Mass of the atom

Almost entirely due to the mass of the nucleus; electrons have very little mass in comparison.

Electric charge of atoms

Atoms are neutral, meaning they have no electrical charge; there is always the same number of positive protons as negative electrons.

Gold foil experiment

An experiment conducted by Hans Geiger and Ernest Marsden in 1911, supervised by Ernest Rutherford, which showed that high-energy alpha particles were deflected.

Rutherford's model of the atom

A model supported by further research that describes the nucleus made up of protons and neutrons, with electrons moving around it.

Ernest Rutherford

A physicist born in New Zealand in 1871, known for his experiments that changed the understanding of atomic structure.

Space in atoms

Huge parts of atoms are empty space; if one atom were expanded to the size of the Sydney Cricket Ground, the nucleus would still be no bigger than a pinhead.

Charge of protons

Protons carry a positive electric charge.

Charge of neutrons

Neutrons are neutral; they have mass but no electric charge.

Deflection of alpha particles

If the 'plum pudding' model of the atom was correct, most high-energy alpha particles would move through gold with only minimal deflection.

Structure of the atom

The current accepted model describes the nucleus containing protons and neutrons, with electrons in the surrounding space.

Subatomic particles

Three types of particles found inside an atom: protons, neutrons, and electrons.

Limitations of Rutherford's atomic model

The model has limitations that were later addressed by more advanced atomic theories.

Discovery of the neutron

The neutron was the last subatomic particle to be discovered among the three subatomic particles.

JJ Thomson

The physicist who discovered that atoms were divisible and made up of smaller particles, known for the plum pudding model.

Positive charge

The charge carried by protons in the nucleus of an atom.

Neutral charge

The charge of neutrons, which have mass but no electric charge.

Negative charge

The charge carried by electrons, which move around the nucleus.

Atomic theory

A theory proposed by Dalton that suggested atoms are indivisible, later revised by Thomson and Rutherford.

Structure of the nucleus

The nucleus is made up of protons and neutrons, which together account for most of the atom's mass.

Proton

A subatomic particle with a positive charge found in the nucleus of an atom.

Neutron

A subatomic particle with no charge found in the nucleus of an atom.

Electron

A subatomic particle with a negative charge that orbits the nucleus of an atom.

Atomic number (Z)

The number of protons in the nucleus of an atom, which determines the element.

Mass number (A)

The total number of protons and neutrons in the nucleus of an atom.

Number of neutrons

Calculated as mass number (A) minus atomic number (Z).

Number of electrons

In its atomic state, the number of electrons is equal to the number of protons.

Relative mass scale

A scale used to compare the mass of atoms, more convenient than actual units.

Periodic table

A table that places elements in order of their atomic number and groups them according to similar properties.

Cobalt

An element with an atomic mass of 59 and an atomic number of 27.

Lithium

An element with 3 protons, 4 neutrons, and 3 electrons, having a mass number of 7.

Oxygen

An element with 8 protons, 8 neutrons, and 8 electrons, having a mass number of 16.

Subatomic particle

A particle smaller than an atom, such as protons, neutrons, and electrons.

Safety risks in experiments

Potential hazards associated with conducting experiments, especially those involving radioactive materials.

Protective measures

Actions taken to ensure safety during experiments, including the use of personal protective equipment (PPE).

Mass of subatomic particles

Proton: 1.007 amu; Neutron: 1.008 amu; Electron: 0.00055 amu.

Investigating atom behavior

The process of comparing the masses of different atoms to understand their properties.

Ignore

A representation of an oxygen atom with mass number 16 and atomic number 8.

Ignore

A conventional representation of an element in the periodic table.

Ignore

A model of an atom of the element lithium.

Rutherford's experiment

An experiment where radioactive particles were fired at gold foil to study atomic structure.

Safety management in experiments

The assessment and implementation of measures to minimize risks during scientific investigations.

Hydrogen

Atomic number 1, Chemical symbol H, Atomic mass 1.01

Helium

Atomic number 2, Chemical symbol He, Atomic mass 4.00

Lithium

Atomic number 3, Chemical symbol Li, Atomic mass 6.94

Beryllium

Atomic number 4, Chemical symbol Be, Atomic mass 9.01

Carbon

Atomic number 6, Chemical symbol C, Atomic mass 12.01

Nitrogen

Atomic number 7, Chemical symbol N, Atomic mass 14.01

Oxygen

Atomic number 8, Chemical symbol O, Atomic mass 16.00

Fluorine

Atomic number 9, Chemical symbol F, Atomic mass 19.00

Neon

Atomic number 10, Chemical symbol Ne, Atomic mass 20.18

Boron

Atomic number 5, Chemical symbol B, Atomic mass 10.81

Sodium

Atomic number 11, Chemical symbol Na, Atomic mass 22.99