Module 3.1 — Electron Theory
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What is electric charge?
A property of particles responsible for electrical interactions.
What is electric current?
Movement of electrically charged particles through a material.
What unit measures electric current?
Ampere (A).
What is static electricity?
An accumulated electric charge that remains in place.
What is an electric field?
A region where an electric charge exerts a force on other charges.
What is electric potential difference?
A difference in electrical potential between two points.
What unit measures electric potential difference?
Volt (V).
What is electromagnetism?
Interaction involving electric charges and magnetic fields.
What is an electrical circuit?
Interconnected components forming a path for electrical operation.
What does a complete circuit path allow?
Charge to flow when a suitable potential difference is applied.
Why must electricity be treated as hazardous?
Excess or misapplied electrical energy can cause injury or death.
What is an element?
A pure substance consisting of one type of atom.
What is an atom?
The basic particle of an element.
What is a molecule?
Two or more bonded atoms, or the smallest independent unit of a substance.
How can a molecule of an element differ from a compound molecule?
An element molecule has one element; a compound has different elements.
What does O₂ represent?
An oxygen molecule containing two oxygen atoms.
What does H₂O represent?
A water molecule containing two hydrogen atoms and one oxygen atom.
What is a compound?
A substance made from different elements chemically combined in fixed proportions.
What is a mixture?
Substances combined without all particles having an identical composition.
What is constant across molecules of a pure compound?
The number of atoms of each constituent element.
Which three particles make up an atom?
Protons, neutrons and electrons.
Where are protons found?
In the nucleus.
Where are neutrons found?
In the nucleus.
Where are electrons found in the BA atomic model?
In shells surrounding the nucleus.
What charge does a proton carry?
Positive (+).
What charge does an electron carry?
Negative (−).
What charge does a neutron carry?
No charge; it is neutral.
How do proton and neutron masses compare?
They have approximately equal mass.
How does electron mass compare with proton mass?
An electron is about 1/1836 of a proton’s mass.
Where is most of an atom’s mass concentrated?
In the nucleus.
Why is a neutral atom electrically neutral?
It has equal numbers of protons and electrons.
How do proton and electron charge magnitudes compare?
Equal magnitude but opposite signs.
What occupies most of an atom’s volume?
Space between the nucleus and outer electron region.
What is an electron shell?
A region around the nucleus occupied by electrons in the BA model.
What are the seven shell labels, from inner to outer?
K, L, M, N, O, P, Q.
Which shell is closest to the nucleus?
K shell.
What formula gives maximum electrons in shell n?
2n², where n is the shell number.
What is the maximum electron count for shell K?
2 electrons.
What is the maximum electron count for shell L?
8 electrons.
What is the maximum electron count for shell M?
18 electrons.
What is the maximum electron count for shell N?
32 electrons.
What is the valence shell?
The outermost occupied electron shell.
What are valence electrons?
Electrons in the outermost occupied shell.
How many electrons are in neutral oxygen?
8 electrons.
How are oxygen’s 8 electrons distributed in the BA diagram?
2 in K and 6 in L.
How many electrons are in neutral copper?
29 electrons.
How many outer-shell electrons does the BA copper example show?
1 valence electron.
How many electrons are in neutral aluminium?
13 electrons.
How many valence electrons does aluminium have?
3.
What determines atomic number?
Number of protons in the nucleus.
What is the atomic number of hydrogen?
1.
What is the atomic number of carbon?
6.
For a neutral atom, how does electron count compare with atomic number?
They are equal.
What is mass number (the BA notes’ simple atomic-mass count)?
Number of protons plus neutrons.
An atom has 6 protons and 6 neutrons. What is its mass number?
12.
An atom has 8 protons and 8 neutrons. What is its mass number?
16.
What changes when an atom gains an electron: element identity or charge?
Charge changes; element identity stays the same.
What are free electrons?
Electrons able to move between atoms within a material.
What is a conductor?
A material in which charge can move relatively easily.
Why do metals generally conduct well?
They contain mobile electrons that can carry charge.
What is an insulator?
A material in which charge cannot move easily.
What makes electron mobility important?
It determines how easily a material can conduct current.
What is electrical conductivity?
A measure of how readily a material permits charge flow.
What charge interaction occurs between two electrons?
They repel one another.
Which listed metal is the best conductor in the BA notes?
Silver.
What happens to glass at very high temperature, per BA notes?
Its electrical conductivity can increase greatly.
Which two conductors are highlighted for aircraft wiring?
Copper and aluminium.
Which conducts better electrically: copper or aluminium?
Copper.
What simple valence-electron rule do BA notes give for conductors?
Typically fewer than 4 outer-shell electrons.
What simple valence-electron rule do BA notes give for insulators?
Typically more than 4 outer-shell electrons.
What is a semiconductor?
A material with conductivity between that of conductors and insulators.
Name two semiconductors mentioned in BA notes.
Silicon and germanium.
How many valence electrons does silicon have?
4.
How many valence electrons does germanium have?
4.
What is a crystal lattice?
A regular repeating arrangement of atoms.
What type of bonding is described in the semiconductor lattice?
Covalent bonding.
What happens to semiconductor electrons when they gain enough heat energy?
Some break free from bonds and can contribute to conduction.
How does increased temperature generally affect intrinsic semiconductor conduction?
It increases because more charge carriers become available.
How does a semiconductor behave near absolute zero?
Almost like an insulator.
Why are covalently bound electrons not free carriers?
They are held in the bond rather than moving through the lattice.
What is ionisation?
Gain or loss of electrons by an atom or molecule, producing an ion.
What is an ion?
An atom or molecule with a net electric charge.
How is a positive ion formed?
An atom loses one or more electrons.
How is a negative ion formed?
An atom gains one or more electrons.
What is a cation?
A positively charged ion.
What is an anion?
A negatively charged ion.
How do electron and proton counts compare in a cation?
Fewer electrons than protons.
How do electron and proton counts compare in an anion?
More electrons than protons.
How is ion charge determined in elementary-charge units?
Number of protons minus number of electrons.
An ion has 8 protons and 10 electrons. What is its charge?
2−.
An ion has 13 protons and 10 electrons. What is its charge?
3+.
What is a monatomic ion?
A charged ion consisting of a single atom.
Which electrons are most involved in forming monatomic ions?
Valence (outer-shell) electrons.
Name three energy sources BA notes associate with electron detachment.
Heat, light and electrostatic fields.
How do like electric charges interact?
They repel.
How do opposite electric charges interact?
They attract.
What can a magnetic field do to a moving ion?
Deflect its trajectory.