CHEMISTRY

Atoms, Elements & the Periodic

Table

•Describe the structure & parts of an atom.

•Identify the properties of an atom.•Interpret information on a periodic table to understand how elements

are grouped.

What are the elements made

of?Element-the simplest pure substance.

Elements are made of atoms, and each element’s atoms are unique to that element

Atoms-the basic building blocks of all matter. They are the smallest particles into which an element can be divided and still be the same substance.

Atoms are made of 3 types of particles-protons, neutrons and electrons

The History of Atomic Theory

Democritus – 440 BCE

Greek Philosopher 2445 years ago.

Called particles that made up “stuff” ATOMS

Atomos (Greek word) “not able to be divided”(uncuttable)small hard particlesConstantly move

Dalton - 1803Atoms make up all substances (the elements)

Atoms can not be created, divided or destroyed.

Atoms combine to make other substances.

Conducted experiments

Dimitri MendeleevProposed the laws of the periodic table

1869-developed the first periodic table

Table was arranged according to increasing atomic weight

Left spaces for elements yet to be discovered

J.J. Thomson - 1897Discovered negatively charged particles in atoms called Electrons.

Conducted Cathode Ray Tube experimentLed to the Plum Pudding Model

Ernest Rutherford - 1909

Discovered the nucleus

Nucleus Small tiny very dense center of atoms

Where most the atoms mass is located

Atoms are mostly empty space where electrons are found

Conducted the Gold Foil experiment

Niels Bohr - 1913Electrons move around the nucleus of atoms in definite paths.

Electrons jump between levels from path to path.

Bohr’s model

Most Recent Atomic Theory

Schrodinger and Heisenberg

Electron paths cannot be predicted.

Electrons are likely to be found in regions around the nucleus called electron clouds.

Called the electron cloud model.

Recent Discoveries

Chadwick • 1932-Discovered that neutrons exist

in the nucleus of atoms• Neutrons have no charge and the

mass equal to protons and help to stabilize the atom

Gell-Mann • 1969-Subatomic particles are made of

smaller particles called quarks

PERIODIC TABLE =ORGANIZED ELEMENTS

Elements are:• PURE-Made of like atoms of that

element• Identified by it’s atomic number (#

of protons)• Arrangement of electrons

determines the elements properties (such as conductivity and reactivity).

Link to videohttp://www.privatehand.com/flash/elements7.swfSelect broadband player.

The Element Song

The Structure of an Atom

Protons – POSITIVE charged particles inside the nucleus (center).

Neutrons – neutral particles inside the nucleus that have NO CHARGE!

Electrons – NEGATIVE CHARGED particles in atoms found around the nucleus.

Atomic ParticlesLocation Charge Mass

Protons Nucleus + positive Heaviest particle

Neutrons Nucleus O Neutral -Similar to a proton but carry no charge

Electrons Orbiting outside the nucleus in electron clouds

- Negative •Lightest particle•Smallest part of an atom

Outside the nucleus

• Can be called a electron cloud, shell, energy level, orbit or ring

• Area outside the nucleus where electrons are found

• 1st cloud=2 electrons• 2nd cloud=8 electrons• 3rd cloud=18 electrons

Boron (B)Atomic #=5Atomic Mass=11

Protons=5Neutrons=6Electrons=5

Sodium-(Na)Atomic #=11Atomic Mass=23

Protons=11Neutrons=12Electrons=11

Energy Levels - Electron Clouds

Regions around the nucleus where electrons are arranged.

Electrons further away from the nucleus have more and more energy.

Each level or cloud can hold a specific # of electrons.

1st level - 2 electrons2nd level - up to 8 electrons3rd level-up to 18 electrons

Valence ElectronsThe electrons in the outermost energy level (electron cloud).

Very important because they determine how an element will react with other substances

What’s in the Box?

Atomic Number

Equals the number of protons inside the nucleus of the atom.

Atomic Number=Number of Protons=the number of electrons

Determines the element.

All atoms of an element have the same atomic number.

No two elements have the same atomic number.

5

B10.81Boron

SymbolAll elements have their own unique symbol

Symbols can be one or two letters

The first letter is always a capital letter

The second is always a lower case letter

Symbols don’t always match their English word bc most are from Latin or Greek roots.

Example: Fe=Iron (English) Ferrum (Latin)

5

B10.81Boron

Mass Number

The total number of protons and neutrons in an atoms nucleus.

Number under the element symbol

Protons + Neutrons = Mass Number

Practice: If an atom has 12 protons, 14 neutrons and 12 electrons, what is its mass number?

Practice online

5

B10.81Boron

Atomic Mass Unit - amu

Unit of measurement for the mass of subatomic particles.

1 amu = 1.7 X 10 -24 They are TEENY TINY!!!

.000000000000000000000017 grams

Proton = 1 amuNeutrons = 1 amuElectrons = almost zero (TINIEST particle with the least mass)Most of the mass is in the nucleus with protons and neutronsOtherwise atoms are mostly EMPTY SPACE

Atomic MassRefers to the weight of the atom.

Atomic Mass= Protons + Neutrons

Never negative

Mass

The Charge of an atom

To find the charge of an atom-

1. Find the number of protons (+)

2. Find the number of electrons (-)• Represent the electrons as a negative

number

3. Add the protons and electrons to find the charge

Ex: Calcium atom has 12 protons and 10 electrons. What is the charge of this atom?

Answer 12 proton + 10 electrons 12 + (-10)= +2This atom would be positive (+)

More practice with charge

What is the charge of a copper atom with 26

electrons?

29 protons (+) + 26 electrons (-)

29-26=+3

positive

What is the charge of a Sulfur atom with 18

electrons?

16 protons (+) + 18 electrons (-)

16-18=-2

negative

ReviewAtoms, which contain

Protons (+), neutrons (o)and electrons (-)

#protons

# neutrons

Mass #

Nucleus-contains protons and neutrons

Electron Cloud-electrons orbit the nucleus

Periodic Table Overview

How the Elements are Arranged

Groups/Families:

Similar properties

Periods/Rows:

Increasing atomic number/mass

Groups/FamiliesColumns of the periodic table that consist of elements that have the same number of valence electrons.

Groups 1 and 2 - same # as groupGroups 13-18 - 10 - the group #Groups 3-12 - no general rule.

PeriodsRows of the periodic table that consist of elements with the same number of electron clouds or energy levels.

Alkali MetalsGroup #1

All metals

1 Valence Electron

Very reactive

Alkaline-Earth Metals

Group #2

All Metals

2 Valence Electrons

Very reactive but less than group #1.

Transition MetalsGroups # 3-12

All metals

1-2 valence electrons

Less reactive than group #2

Also contain lanthanide and actinide series (radioactive/unstable).

Groups # 13-16Elements change from metals to nonmetals and include the metalloids.

Atoms have 10 fewer valence electrons than the group #.• Boron Group #13 - 3 valence

electrons• Carbon Group #14 - 4 valence

electrons• Nitrogen Group #15 - 5 valence

electrons• Oxygen Group #16 - 6 valence

electrons

HalogensGroup 17

All nonmetals

7 valence electrons

Very reactiveOnly need to gain 1 more electron.

Noble GasesGroup # 18

All nonmetals

8 valence electrons - except helium only has 2.

UnreactiveHave a full outer electron cloud (energy level).

Hydrogen stands alone

1 valence electron

Very reactive

Reacts violently with Oxygen under the right conditions.

Everyday Uses

IsotopesAtoms of elements that have the same number of protons (atomic number) but a different number of neutrons inside the nucleus.

IonsCharged particles that form during chemical changes.

Form when one or more valence electrons are transferred from one atom to another.

Ions are Charged! + or -

Atoms that lose electrons become positive ions.

Atoms that gain electrons become negative ions.

Cl gains an electron from Na to form NaCl -

Cl ion is negative - more electrons (-)

Na ion is positive - more protons (+).