chapter 4 Atoms
What is a model?
Uses familiar ideas to explain unfamiliar facts observed in nature. Model Uses familiar ideas to explain unfamiliar facts observed in nature. It can be changed if you get new info.
You get a mental picture or a model of the object. INDIRECT EVIDENCE Evidence you get about an object without actually seeing or touching the object. You get a mental picture or a model of the object.
Greek Model In the 5th century BC, Democritus believed that matter could be divided into smaller & smaller pieces forever until you got to the smallest possible piece called an atom (uncuttable).
Daltons Model In 1803, Dalton published his atomic theory from studying weather & the composition of air.
_____ _ _______ 1) All matter is made of atoms 2) Different elements have different kinds of atoms 3) Compounds are formed by joining atoms of 2 or more elements.
Invented the Plum Pudding Model Thomson's Model He discovered the electron & figured it was part of an atom. Invented the Plum Pudding Model The atom was a positively charged ball with lots of negatively charged electrons stuck into it like “plums in pudding.”
In 1908, Rutherford discovered the nucleus. _________ _ ____ In 1908, Rutherford discovered the nucleus. He stated that the atom was mostly empty space made up of a positively charged nucleus with negative electrons scattered around it.
Rutherford’s Experiment In his experiment, Rutherford fired a stream of alpha particles at a sheet of gold foil and found that: Most of the bullets passed right through the gold sheet without changing course which meant that the gold atoms were made up of empty space.
2. Some bullets bounced back from the sheet which meant that like charges repel. The alpha particles were positive so the nucleus must then be positively charged.
Bohr fixed up Rutherford’s theory. Bohr’s Model Bohr fixed up Rutherford’s theory. He stated that electrons orbited the nucleus on definite paths like the planets around the sun.
The Wave Model Based on a prediction of where the electrons actually are using math formulas. Basic idea of waves.
Subatomic Particles- particles smaller than an atom 4-2 Structure of Atom Subatomic Particles- particles smaller than an atom 3 Main Subatomic Particles: Protons, Neutrons, Electrons
Nucleus The tiny center of atom 99.9% of atom’s weight is the nucleus but it is 100,000 times smaller than the entire atom. Like a bee in Yankee Stadium
Protons Positively Charged particles (+) Found in nucleus Weighs 1 AMU
Neutrons Neutral particles Found in nucleus Weighs 1AMU+
AMU ATOMIC MASS UNIT Special unit used to measure the mass of subatomic particles. 1 proton = 1AMU
Atomic Number Number of protons in nucleus of atom Determines what the element is
Hydrogen’s Atomic number is 1 = 1 proton Carbon’s Atomic Number is 6 = 6 protons
Isotopes Atoms of same element that have the same number of protons but a different number of neutrons C12- C14- difference- 2 more neutrons
MASS NUMBER Sum of protons & neutrons distinguishes one isotope from another Carbon = Mass# 12 6P + 6N= 12 total.
Uranium238 146N + 92P = 238 Uranium235 143N + 92P = 235
Atomic Mass Average mass of all isotopes of that element, usually a decimal located on the bottom of each card. Atomic mass of carbon=12.011
Electrons Number of protons = number of electrons outside nucleus. Electron fills cloud. Electrons can be anywhere within the space around nucleus
Electrons are arranged in energy levels according to how much energy they contain Electrons with lowest energy are in level closest to nucleus.
Electrons with high energy are in levels farther from nucleus. Each level can only hold so many electrons: 1st-2 2nd-8 3rd-18 4th-32 5th-18
Chemical makeup Properties of elements depend on how many electrons are in the various energy levels. Bonding: some do/some don’t Quarks-3particles that make up protons & neutrons