The Atom

What is Matter?

• anything that has mass and takes up space

• matter is made up of atoms

How Small are Atoms?• It would take a stack of about 50,000 aluminum atoms

to equal the thickness of a sheet of aluminum foil from your kitchen

• If you could enlarge a penny until it was as wide as the US, each of its atoms would be only about 3 cm in diameter – about the size of a ping pong ball

• A human hair is about 1 million carbon atoms wide • A typical human cell contains roughly 1 trillion atoms• A speck of dust might contain 3x1012 (3 trillion) atoms • It would take you around 500 years to count the

number of atoms in a grain of salt

Results

• How many cuts were we able to make?• Do you think we could keep cutting the

paper forever? Why or why not?• You would have to cut the paper in half

around thirty-one (31) times to get to the size of any atom.

What is an Atom?• the smallest unit into which

matter can be divided

• building blocks of all matter

• comprised of a nucleus (at it’s center) and an electron cloud (surrounding the nucleus)

• made up of sub-atomic particles

• smaller than an atom• protons • neutrons• electrons

What are Subatomic Particles?

Early Atom Models:What is the

Rutherford Model?

• mostly empty space

• small, positive nucleus

• contained protons

and electrons scattered around the outside

Early Atom Models:What is the Bohr

Model?

• electrons move in definite orbits around the nucleus

Modern Atom Model: What is the

The Electron Cloud Model?

• sometimes called the wave model

• spherical cloud of varying density

• varying density shows where an electron is more or less likely to be

What are Protons?

• positively charged particles (+)

• help make up the nucleus of the atom

• equal to the atomic number of the atom

• contribute to the atomic mass

• equal to the number of electrons

+

+

+++

+++

-

-

-

-

--

-

- +

What are Neutrons?

• neutral particles; have no electric charge

• help make up the nucleus of the atom

• contribute to the atomic mass

+

+++

+++

-

-

-

-

--

-

- +

What are Electrons?

• negatively charged particles (-)

• found outside the nucleus of the atom in the electron orbits/levels

• each orbit/level can hold a maximum number of electrons

• 1st orbital = 2 electrons• 2nd orbital = 8 electrons• 3rd orbital = 8 electrons

+

+++

+++

-

-

-

-

--

-

- +

-

What are Electrons?

• move so rapidly around the nucleus that they create an electron cloud

• mass is insignificant when compared to protons and neutrons

• equal to the number of protons

• involved in the formation of chemical bonds

+

+++

+++

-

-

-

-

--

-

- +

-

What are Valence Electrons?

• found in the outermost energy level of the electron cloud (called the valence shell)

• involved in bonding

• determine the chemical properties of an element

Notice that the electrons are not apart of the nucleus

-+

++-

-

-

Protons and neutrons are grouped together to form the “center” or nucleus of an atom

How is the Atom’s Center Formed?

Atomic Structure

How are Atoms Described?

• atomic number = number of protons

• in a neutral atom, the # of protons = the # of electrons

• atomic mass= the number of protons + the number of neutrons

What is Atomic Number?

• the number of protons in the nucleus of an atom

+ ++

-

-

-

What would be the atomic number of this atom?

What is the Atomic Mass?

• the total number of protons and neutrons in an atom’s nucleus

• expressed in Atomic Mass Units (amu)– each proton or neutron

has a mass of 1 amu

+ ++ -

-

-What would be the atomic

mass of this atom?

+ 3 4

3 protons + 4 neutrons = an atomic mass of 7 amu

Why did we not account for the electrons when calculating the

mass number?

Hydrogen (H) Atom• Let’s use the Bohr Model to sketch a hydrogen

atom.• notice the one electron in the first orbital

+

-

+

-

= 1

= 0

= 1

P = Atomic # =E = P =N = Atomic Mass – Atomic # =

Oxygen (O) Atom• notice the two electrons in the first orbital/level and

the six in the second

P = Atomic #________ E = P________N = Atomic Mass – Atomic #

________

Bohr Diagram

Sodium (Na) Atom• notice the two electrons in the first orbital/level, eight in

the second, and one in the third

P = E =N =

Bohr Diagram

Building AtomsUsing the whiteboard and the proton, neutron, and

electron pieces, build the following atoms, and determine their atomic and mass numbers.

Atoms Protons Neutrons ElectronsCarbon 6 6 6Beryllium 4 5 4Oxygen 8 8 8Lithium 3 4 3Sodium 11 12 11