Atoms: Building Blocks of Matter

Structure of an Atom

• Subatomic particles: 3 particles that make up an atom (protons, neutrons, electronselectrons)

–Nucleus: made up of protons and neutrons in center of atom

Proton: positively charged particle

Neutron: particle with no charge

–ElectronsElectrons: negatively charged particles around the nucleus

All protons are alike, all neutrons are alike, and all electrons electrons are alike even in different substances!

Structure of an Atom

Atomic Models

Greek ModelGreek Model:: original idea of matter made of particles

–Atomos:

“not to be cut”

or indivisible

Atomic ModelsJohn Dalton ModelJohn Dalton Model: 18031803

All elements (gold, silver, hydrogen,

oxygen,…) are made of atoms

Atomic Theory and Models

Dalton thought that atoms were like smooth, hard spheres that could not be broken into smaller pieces.

Atomic Models Dalton ModelDalton Model:

Atoms of the same element are

exactly alike

Atoms of different elements are

different

Atomic Models Dalton ModelDalton Model:

Compounds: formed by the joining

of atoms of 2 or more elements

J.J. Thomson and his cathode J.J. Thomson and his cathode ray experiment 1897ray experiment 1897

Atomic Theory and Models•Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere.

Also known as the “plum pudding” model

Ernest Rutherford’s Gold Foil Ernest Rutherford’s Gold Foil Experiment 1908Experiment 1908

Most of the particles went directly through the foil!

Atomic Theory and Models

Rutherford was surprised that only a few positive particles were deflected strongly. This led him to conclude that atoms had positively charged particles in the nucleus.

Atomic Theory and Models

Since many particles passed right through the foil sheet, he also concluded that the atom must have a lot of space separating the nucleus from the electrons.

Atomic Theory and Models

Through the early twentieth century, atomic models continued to change.

Niels Bohr ModelNiels Bohr Model: 19121912

Niels Bohr suggested that electrons move in specific orbits around the nucleus of an atom

Cloud ModelCloud Model: 19271927

Electrons move rapidly in every direction around

the nucleus

Atomic Theory and Models

Modern Atomic ModelModern Atomic Model:

The nucleus, which contains both protons and neutrons, is surrounded by a cloudlike region of electrons.

Atomic Theory and Models

• Let's see what Tim and Moby have to say about Atomic Models

Design of periodic table

• Periodic Table: A classification system for elements

Atomic number 7979

AuAu chemical symbol

GoldGold 196.967 196.967 common name

Atomic mass

Characteristics of Atoms

• Atomic Number: number of protons in each element

Hydrogen = 1 Helium = 2 Oxygen = 8 Nitrogen = ___

Look at periodic table of elements in your agenda or on the back cover of your book

Characteristics of Atoms

• AMU: special unit to measure the mass of atoms

–One proton = one AMU–One neutron = one AMU

0.00000000000000000000000167 g

–Electrons have no mass0.0000000000000000000000000911 g

Using your periodic table, answer the following.

How many protons does Krypton have?

a) 84 b) 36 c) 83 d) 48

How many electrons does Krypton have?

a) 84 b) 36 c) 83 d) 48

How many neutrons does Krypton have?

a) 84 b) 36 c) 83 d) 48

Using your periodic table, answer the following.

How many protons does Silver have?

a) 107 b)61 c) 108 d)47

How many electrons does Silver have?

a) 107 b)61 c) 108 d)47

How many neutrons does Silver have?

a) 107 b)61 c) 108 d)47

Electrons• Each electron is in an energy level

• The higher the energy level = the farther the distance from the nucleus

• Inside level holds 2 electrons

• The 2nd level holds 8 electrons• The 3rd level holds 8 electrons (it CAN hold 18)

• The number of electrons in the outer “shell” or “orbit” determines how it will act and react to other substances

Drawing Bohr Models of the AtomRemember the Bohr Model?

Even though the “Cloud” model is the most accurate, we cannot diagram atoms easily in 3-D.

We use Bohr’s model to illustrate which energy levels the electrons are located in.

Examples of Bohr Diagrams

• Build a Bohr Diagram

SodiumWhich element?

Atom GameAtom GameEach person represents a subatomic particle:Each person represents a subatomic particle:

Proton = Red Proton = Red Neutron = BlueNeutron = Blue Electron = YellowElectron = Yellow

In your group, please construct the following In your group, please construct the following atoms – help each other!atoms – help each other!

- Oxygen – O - Sodium - Na - Oxygen – O - Sodium - Na - Silicon – Si - Beryllium – Be- Silicon – Si - Beryllium – Be

- Chromium – Cr - Titanium - Ti - Chromium – Cr - Titanium - Ti

Valence Electrons and Bonding

All elements are most stable when there are 8 electrons in their valence shell

The number of valence electrons in an atom determines which elements it can bond with.

Valence electrons are those electrons that have the highest energy level and are held most loosely.

• Isotopes– Atoms of the same element have the same

number of protons but have different numbers of neutrons

• Example of isotopes:– Hydrogen: