Physical Science Chapter 6.1 The Atom Physical Science Chapter 6.1

Fundamental Particles and Forces C6.1 Atoms are the smallest elemental particle Made of protons neutrons and electrons 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.