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Chapter 5Atoms: Building Blocks of Matter
EvidenceDirect evidence is when you do something to gather the evidence
Examples are Doing an experiment
Reading a book
Indirect evidence is when you do not see or touch the subject
Examples areHearing from someone else
The Greek ModelAll elements could be seen and touched
No element was smaller then what could be seen
The four elements are fire, earth, wind and water
DemocritusCalled the Greek model (over 2000 years ago)
Named the smallest piece of matter the atomFrom the Greek word atomos meaning not to be cutAtomists – the philosophers who agreed w/ DemocritusHypothesis – small hard particles made up of same material in all shapes and sizes, never ending amount, always moving, capable of joining together
Dalton’s Model
John Dalton (Early 1800’s)Atomic Theory
All elements are composed of atoms, atoms are indivisible and indestructible particlesAtoms of the same element are exactly alikeAtoms of different elements are differentCompounds are formed by joining of atoms of two or more elementsBecame foundation of atomic theory
Thomson’s Model
J.J. Thomson (1897)Discovered that a particle smaller then the atom had to existThese were negatively charged particles - electronPlum Pudding model
Atom was made up of a pudding like positively charged material throughout which negatively charged electrons were scattered
Thomson’s ModelRaisin Pudding
RutherfordErnest Rutherford (1911)
Conducted an experiment in which some positive particles went through gold foil and others bounced off
Proposed that atoms have a small positively charged center - nucleusAll the positively charged particles are found in the nucleus and all the negatively charged electrons were scattered outside the nucleus around the edges
Rutherford’s Model
Bohr ModelNiels Bohr (1913)
Wanted to know where Rutherford’s electrons were located – believed that the negative and positive particles were held together because of their attraction
Bohr placed each electron in a specific energy level
Electrons move around in definite orbits around the nucleus – these orbits are located certain distances from the nucleus
Bohr’s Model
Wave ModelWave mechanics – today’s atomic theory is based from wave mechanics
Electrons – do not move about the atom in a definite pattern - it is actually impossible to predict the location of the electrons
An atom has a small positively charged nucleus surrounded by a large region where electrons are making the atom neutral – this region is mostly empty space
Atom
Composed of subatomic particles – particles smaller than an atom
Proton – positively charged particles
Neutron – no charge
Electrons – negative charge
Nucleus – center of the atom
Modern Atom
NucleusThe core of the atom
Contains 99.9 percent of the mass of the atom but is smaller then the entire atom
Protons and neutrons located in the nucleus
Unit of measurement for subatomic particles is Atomic Mass Unit - amu
Atomic NumberThe number of protons in the nucleus is called the atomic number
The atomic number identifies the element
This number will never change
MassAll atoms have a mass number
The mass number of atom is the sum of the protons and neutrons
The number of protons is the atomic number so if you have the mass of an element you can find the number of neutrons that make up the mass
Uranium 235 – proton number is 92 – neutron number is 143
Mass number 9, atomic number 4 – what is the # of neutrons
Atomic Mass – the average mass of all isotopes that occur naturally for that element
IsotopesAtoms of the same substance that have the same number of protons but different numbers of neutrons are called isotopes.
name symbol A Z neutronsnitrogen-12 isotope 12 7
5nitrogen-13 isotope 13 7
6nitrogen-14 isotope 14 7
7nitrogen-15 isotope 15 7
ElectronsElectrons are negatively charged and have an amu of .0006
The exact location of a electron is not known
The location in which the electron can be found is the electron cloud
The electrons seem to be locked into a certain area based on its energy level
Energy LevelsRepresents the likely location for an electron in the electron cloud
Electrons with the lowest energy are found in levels near the nucleus
The higher the energy of the electron the farther away from the nucleus
Each energy level can only hold a certain number of electrons
Properties of elements depend on number of electrons in outer energy level.
QuarkCurrent theory states that the different parts of the element are made up of quarks
There are a number of different kinds of quarks
Quarks have properties called flavor and color – there are six different flavors and three different colors
Forces within an atom
Four forces account for the behavior of an atom
Electromagnetic force – either attracts or repels particles – electrons are kept in orbit by this force
Strong Force – opposes the electromagnetic force – “glues” protons together
Weak force – responsible for radioactive decay
Gravity – weakest force – not entirely known how it affects an atom
HydrogenAtomic number of hydrogen is 1
One proton in the nucleus
no neutrons
Review1. Carbon 14 and carbon 12 – what is the difference?
2. What is the mass number of an element with 16 protons, 17 neutrons, and 16 electrons?
3. If an elements atomic number is 12, what does its nucleus contain?
4. How many neutrons are in an element with a atomic number of 4 and a mass number of 9?
Questions
Go back through your notes and if there is anything you are unsure of ask now!!!!!!!!