Chapter 6.1: The Atom, Fundamental Particles and Forces

G8 Physical Science

C6.1 Fundamental Particles and Forces

• Supplies: pencil and science notebook• Standards:– 3a: Students know the structure of the atom and

know it is composed of protons, neutrons, and electrons

– 7b: Students know each element has a specific number of protons in the nucleus (atomic number) and each isotope of an element has a different specific number of neutrons in the nucleus.

C6.1 Fundamental Particles and Forces

• You will be taking notes using the Cornel Notes format or the Charting Notes format.

C6.1 Fundamental Particles and Forces

• Definitions• Electric charge – a fundamental property of

matter that comes in two types called positive and negative

• Elementary charge – the smallest unit of electric charge that is possible in ordinary matter represented by the lowercase letter e.

C6.1 Fundamental Particles and Forces

• More Definitions• Neutral – a condition where the total positive

charge is canceled by the total negative charge. Matter is neutral most of the time.

• Charged – a condition where there is an excess of positive or negative charges

• Static electricity – the buildup of either positive or negative charges; made up of isolated, motionless charges.

C6.1 Fundamental Particles and Forces• Yet More Definitions• Electron – a particle with an electric charge (-e)

found inside the atom but outside of the nucleus• Proton – a particle with an electric charge (+e)

found in the nucleus of an atom• Neutron – a particle with zero charge found in

the nucleus of atoms• Nucleus – the tiny core at the center of an atom

containing most of the atom’s mass and all of its positive charge

C6.1 Fundamental Particles and Forces

• Even More Definitions• Atomic number – the number of protons in the

nucleus. The atomic number determines what element the atom represents.

• Isotopes – atoms of the same element that have different numbers of neutrons in the nucleus

• Mass number – the number of protons plus the number of neutrons in the nucleus

C6.1 Fundamental Particles and Forces

• The last of the Definitions (in C6.1)• Stable – a nucleus is stable if it stays together• Radioactive – a nucleus is radioactive if is

spontaneously breaks up, emitting particles or energy in the process

Atoms as Building Blocks• Atoms is the smallest elemental particle.• Lego Analogy - we build with certain units that are

all different. If we break up the units we have plastic.• We build things with atoms. Each element is

different. If we break them up we have protons, neutrons, and electrons.

Electric Charge

• Electrical charge is a fundamental property of matter, positive and negative charges

• Opposites attract, likes repel

• Elementary charge, (electrical) use symbol e

• Units of e, +2, +2e, -e, -3, no partial e’s

Static Electricity Neutral -- electrical charge of

zero Charged means the electrical

charge is not zero, it is positive or negative

To find a charage, add all the positive charges and subtract all the negative charges

Static electricity is a tiny imbalance of positive or negative charge. Friction pulls a charge off of one object and temporarily puts it on another object

Static Electricity Demo

• Volunteer with long hair• A balloon

• Hair has a positive charge• Balloon has a negative charge

History of Atomic Discovery

450 BC. Greece, Democritus - Matter is discontinuous and can not be infinitely divide. At some point an fundamental indivisible particle would emerge. Aristotle did not believe him. Aristotle won the debate.

1803 England, John Dalton – Matter is discontinuous. Boyle (1620) had proven that gas was made of small particles. Dalton proposed that everything is. Also cited Lavoisier (law of conservation of matter) and Proust (law of definite composition – two volumes of the same stuff have the same mass)

History of Atomic Discovery• 1897, England, J.

J .Thompson discovered small negatively charged particle, electrons (-) Thought it was stuck into atom like plum pudding.

• 1911, England (originally New Zealand), Rutherford, shot helium ions at gold foil -- lots of holes (expected, he knew atom was mostly space), some solid parts, protons (+)

• 1832 Chadwick, discovers neutron, no charge

Your Turn• Write down the

name of two elements – remember, an element is a pure substance that contains only one kind of atoms

Three subatomic particles• Electron, outside the

nucleus in the electron cloud, negative charge, mass 9.09 X 10-28

• Proton, inside nucleus, positive charge, mass 1.637 X 10-24

• Neutron, inside the nucleus, no charge, mass 1.675 X 10-24

• Electron:proton• 1:1000• softball: football field

Forces Inside Atoms• Electromagnetic, neutron &

protons, balanced by kinetic energy.

• Strong nuclear force, keeps protons together, stronger than repulsion but for short, nucleus distance.

• Weak force, holds proton and electron together to make a neutron.

• Gravity, weaker than weak force, but not distance limit. Combines well.

How do atoms differ?• Number of protons, defines

the atom, atomic number -> 1

• Each element has a unique atomic number (whole number)

• Complete atom has same number of protons, neutrons, and electrons. Electrically neutral.

• Atomic mass (weighted average) -> 1.00197 (see next slide)

Your Turn

• Find out how many protons and electrons are in a balanced atom of your element.

Isotopes

• Isotopes are atoms that have the same number of protons but a different number of neutrons

• Mass number is the number of protons plus the number of neutrons. Isotopes have the same atomic number but different mass numbers.

Radioactivity• Radioactive atoms have an unstable nucleus. Atom will try to

become stable by– Alpha decay -- nucleus ejects two protons and two

neutrons (helium nucleus)– Beta decay -- Neutron splits into a proton and an electron– Gamma decay -- nucleus gets rid of excess energy, number

of protons and neutrons stay the same.