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TEKS 8.5A describe the structure of atoms including the masses, electrical charges and locations, of protons and neutrons in the nucleus and electrons in the electron cloud

TEKS 8.5B identify that protons determine an element’s identity and valence electrons determine its chemical properties, including reactivity

Each element on the Periodic Table is made of the same kind of atom.

Each atom in an Each atom in an element has the element has the same number of same number of

protons. .

The number of protons The number of protons present in the atom is present in the atom is what determines the what determines the

element’s identity and and is shown by the is shown by the atomic

number.

On your Periodic Table, fill in On your Periodic Table, fill in this information.this information.

# protons = element’s identity = atomic number

Atoms are made up Atoms are made up of smaller of smaller

particles called called protons, , neutrons

and and electrons..

Each particle in the Each particle in the atom has specific atom has specific

properties, such as properties, such as location, location, electric

charge and mass. and mass.

Structure of Structure of the Atomthe Atom

The NucleusThe NucleusThe center of the atom is called the nucleus .

proton

neutron

nucleus

3

Li

6.941Lithium

The nucleus contains protons and neutrons.

Since each proton and Since each proton and neutron in the nucleus has a neutron in the nucleus has a mass of mass of 11 atomic mass unit atomic mass unit (amu), we can (amu), we can add the the number of protons and number of protons and neutrons together to find the neutrons together to find the atomic mass. .

Fill in this information on your Fill in this information on your Periodic Table!Periodic Table!

# protons + # neutrons = atomic mass

How many protons are in the element lithium?

Lithium has 4 neutrons, what is its atomic mass?

3

7

The Periodic Table shows the The Periodic Table shows the mass for each element as a mass for each element as a decimal. When we use the . When we use the atomic mass to find the atomic mass to find the number of protons or number of protons or neutrons, we neutrons, we round the the mass number.mass number.

If the mass number is If the mass number is known, and you know the known, and you know the number of protons, how number of protons, how can you find the number can you find the number of neutrons? of neutrons? Mass # - Mass # - #protons = =

#neutrons#neutrons

fill in this information on fill in this information on your Periodic Tableyour Periodic Table

Atomic mass - # protons = # neutrons

Surrounding the nucleus is an area called the electron cloud. Inside the electron

cloud, electrons orbit around in different energy levels.

energy levels

The electrons are so small that they basically have no mass, so they are not included in finding

the atomic mass.

electron

neutron

proton

As a general rule, each energy level only As a general rule, each energy level only holds so many electrons at a given time. holds so many electrons at a given time.

The The first energy level, which is closest energy level, which is closest to the nucleus, holds up to to the nucleus, holds up to 2 electrons. electrons.

The The second energy level holds up to energy level holds up to 8 electrons.electrons.

The The third energy level may hold energy level may hold 8 or or more electrons.more electrons.

first energy level

second energy level

third energy level

8 or more!

How many electrons are in each energy

level of the element Lithium? 1st – 2, 2nd –

1electron

energy levels

3

Li

6.941Lithium

electron cloud

By numbering the periods (rows) on the Periodic Table, you can determine how many energy levels are in an atom. For example, Lithium is in period 2, therefore it has 2 energy levels.

Number the first three periods on your Periodic Table.

How many energy levels does sodium contain?

Period 3, 3 energy levels

Valence ElectronsValence ElectronsThe numbers of electrons in an atom’s outermost energy level are called valence electrons.

Valence electrons…..

valence electrons are found here!

These electrons are These electrons are important because they important because they determine how determine how reactive the element is with other the element is with other

elements. elements.

For example, Lithium has only 1 valence electron. Since the second energy level may hold up to 8 electrons, Lithium would need 7 additional electrons in order for its outermost energy level to be filled. But, it is easier for Lithium to give away 1 electron instead of finding 7. Lithium is highly reactive!!

Charges on particlesCharges on particles

Protons carry a Protons carry a positive electric charge.electric charge.

Electrons carry a Electrons carry a negative electric charge.electric charge.

Neutrons have Neutrons have no charge. charge.

The most stable form of an atom is electrically neutral. This means that the number of protons and electrons is equal.

For example, look at the element oxygen. Oxygen is atomic number 8, which means it has 8 protons (+).

Therefore, in a stable oxygen atom, there are 8 electrons (-). The positive and negative charges are balanced.

6

Look at your Periodic Table. Find the element Carbon.

How many positive (protons) charges does carbon have?

How many negative How many negative charges (electrons) charges (electrons) does carbon have? does carbon have?

6

What is the mass of carbon? 12.0112

How can the number of neutrons be determined? (atomic mass - # protons = #

neutrons)

Carbon has 6 neutrons.

Write this on your Periodic Table.

Atomic mass - # protons = # neutrons