Things to know for tomorrow’s quiz… Static electricity Cathode ray experiment Thomson model Gold foil experiment Rutherford model Democritus/Aristotle Dalton and Dalton models Counting Atoms Conservation of Mass Balancing Equations

Review Questions…

Static electricity… what are the 3 methods?

Atomic Theory History Dalton Thomson Rutherford Bohr If the nucleus of an atom is positively charged, and there are negatively charged electrons going around it, why do the electrons not crash into the nucleus?

Niels Bohr (1913) Niels Bohr experimented with gas discharge tubes and came up with an explanation of why different elements produced different colours.

Electrons must occupy orbits (sometimes called orbitals, or energy shells. Electrons stay in their orbits, unless they are excited by electricity or heat. If that happens, they can jump to another orbit. When they return to their original orbit, they give off a specific wavelength of light.

Bohr-Rutherford Diagram Rules This is a representation of the atom that shows the number of protons in the nucleus, as well as the number of electrons in each orbit. A maximum of 2 electrons can fit in the first orbit. A maximum of 8 electrons can fit in the second orbit. A maximum of 8 electrons can fit in the third orbit.

VERY IMPORTANT TIP: The atomic number of an element shows you how many protons and electrons there are (# of protons = # of electrons).

Important Additional Rule: If an atom has 9 electrons, can they be distributed randomly into any of its orbitals? An orbital must be filled to capacity with electrons before we begin to assign electrons to another orbital.

Steps to drawing Bohr-Rutherford Models Ex: Mg

Quick review Number of protons: ______ Number of electrons: ______ Atomic mass: ______

James Chadwick, 1932 James Chadwick discovered the ___________ in 1932. He concluded that the neutron is part of the nucleus and helps to stabilize the atom. A neutron has slightly more mass than a proton.

Actual charges and masses: Particle Electric charge Mass (g) Proton 1.6726 × 10-24 Neutron 1.6749 × 10-24 Electron 9.1094 × 10-28

True or false? The number of neutrons in a nucleus is the same as the number of protons.

Draw a Bohr-Model for Lithium Lithium must have _____ protons. Lithium must have _____ electrons Lithium should have _____ neutrons

Very important! Atoms of the same element MUST have the same number of protons as each other. For example, ALL lithium atoms MUST have 3 protons. Atoms of the same element DO NOT necessarily have the same number of neutrons. For the lithium example, most atoms have 4 neutrons, but some have 3

Isotopes Atoms of the same element with different number of neutrons are called _____________. The number of neutrons plus the number of protons is called the ________________ (electrons have little effect on mass)

Notation for Boron-10 and Boron-11 Mass number Atomic number

Notation for Boron-10 and Boron-11 Mass number Atomic number

SAM = Simplified Atomic Model This is like writing a Bohr- Rutherford model, but quicker. It also shows the number of neutrons, so you need to be provided with the mass number.

Fluorine-19 Chlorine-37

Potassium-39