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!!!!!!!!