Objectives• I will know the charges and locations

of protons, neutrons and electrons in an atom

• I will be able to determine how many protons, electrons and neutrons are in an element and explain how to determine the number of protons, electrons and neutrons

What is an atom?• Atom: the smallest unit of matter that retains the identity of the substance

• First proposed by Democratus.

Atomic Structure• Atoms are composed of 2 regions:

• Nucleus: the center of the atom that contains the mass of the atom

• Electron cloud: region that surrounds the nucleus that contains most of the space in the atom

NucleusElectron

Cloud

What’s in the Nucleus?• The nucleus contains 2 of the 3

subatomic particles:• Protons: positively charged subatomic particles

• Neutrons: neutral subatomic particles

*Protons and neutrons have the same mass.

What’s in the Electron Cloud?

• The 3rd subatomic particle resides outside of the nucleus in the electron cloud

• Electron: the subatomic particle with a negative charge and relatively no mass

How do these particles interact?

• Protons and neutrons exist compacted in the tiny positively charged nucleus accounting for most of the mass of the atom

• The negatively charged electrons are small and have relatively no mass but occupy a large volume of space outside the nucleus

How do the subatomic particles balance each other?• In an atom:

• The protons = the electrons• If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral

• The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

Suggestion….

Open your textbook or your agenda to the page containing a periodic table of elements (132-133).

How do we know the number of subatomic particles in an atom?

• Atomic number: this number indicates the number of protons in an atom• Ex: Hydrogen’s atomic number is 1

• So hydrogen has 1 proton• Ex: Carbon’s atomic number is 6

• So carbon has 6 protons

**The number of protons identifies the atom.

Ex. 2 protons = He, 29 protons = Cu

Think Pair Share• With your partner, find the atomic

number of each element has:• Student A: Carbon (C)• Student B: Potassium (K)• Student A: Beryllium (Be)• Student B: Helium (He)

**After you have completed your element, share with your group.

• Mass number: the number of protons and neutrons in the nucleus

• Ex: Silicon can have a mass of 28. Since it has 14 proton it must have 14 neutrons

• # of neutrons = mass # - atomic #

How do we know the number of subatomic particles in an

atom?

Determining the number of protons and neutrons

• Li has a mass number of 7 and an atomic number of 3• Protons = 3 (same as atomic #)• Neutrons= 7-3 = 4 (mass # - atomic #)

•Ne has a mass number of 20 and an atomic number of 10• Protons = 10• Neutrons = 20 - 10= 10

Try this example on your own!:

Let’s check out Calcium (Ca)!

Calcium’s Atomic Number =

Calcium’s Atomic Mass =

Calcium’s Neutrons =

20

40

20

Think Pair Share• Decide how many protons and

neutrons each element has.• Student A: Carbon (C)• Student B: Iodine (I)• Student A: Silicon (Si)• Student B: Iron (Fe)

What about the electrons?• The electrons are equal to the

number of protons• So e- = p+ = atomic #

• Ex: Li has a mass # of 7 and an atomic # of 3• p+ = 3• no = 4• e- =3

Easy peasy lemon squeezy!…

Think Ink Share• Write your answers to the

following and then share with your partner.

• How many electrons does Mercury (Hg) have?

• Barium (Ba)?• Titanium (Ti)?

Determine the number of subatomic particles (all 3) in the following:Examples:1. Find Chlorine (Cl)• Cl has a mass # of 35 and an atomic

# of 17• p+ = 17, no = 18, e- = 17

• K has a mass # of 39 and an atomic # of 19• p+ = 19, no = 20 e- = 19

Think Ink Share• Write your answers and then share

with your partner.• Find the number of protons, neutrons

and electrons of the following:• Titanium (Ti)• Nickel (Ni)• Copper (Cu)

How exactly are the particles arranged?

• Bohr Model of the atom: All of the protons and the neutrons

The 1st ring can hold up to 2 e-

The 2nd ring can hold up to 8 e-

The 3rd ring can hold up to 18 e-

What does carbon look like?

Mass # = 12 atomic # = 6

p+ = 6 no = 6 e- = 6

6 p and 6 n exist in the nucleus

Exit Ticket

• Explain how we know the number of protons, electrons, and neutrons there are in the element Copper.