Friday, Oct. 25th: “A” DayMonday, Oct. 28th: “B” Day

AgendaFinish section 3.2: “Structure of Atoms”

Atomic number, mass number, isotopeMovie: “Writing Nuclear Symbols” and worksheetHomework:

Sec. 3.2 review, pg. 89: #1-8Finish movie worksheetConcept Review: “Structure of Atoms”

Atomic Number is the Number of Protons in the Nucleus

Atomic Number: the number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element.

No two elements can have the same atomic number.

The Atomic Number Also Tells the Number of Electrons

The atomic number also reveals the number of electrons in an atom. Why?

For atoms to be electrically neutral, the number of positively charged protons must equal the number of negatively charged electrons.

If you know the number of protons in an atom, you automatically know the number of electrons too!

Mass Number is the Number of Particles in the Nucleus

Mass Number: the sum of the numbers of protons and neutrons of the nucleus of an atom. (also called atomic mass)

Protons + Neutrons

Mass Number

Unlike the atomic number, the mass number can vary between atoms of a single element.

Atomic Number/Mass Number

Sample Problem A, pg. 86How many protons, electrons, and neutrons

are there in an atom of copper whose atomic number is 29 and whose mass number is 64?

Atomic number = number of protons = 29Protons = electrons = 29Mass number = protons + neutrons64 = 29 + Neutrons

Neutrons = 35

Practice Problem #3, pg. 86Calculate the mass number for an atom that has 45

neutrons and 35 electrons.

Mass number = protons + neutronsProtons = electrons = 35Mass number = 35 + 45

Mass number = 80Which element is this?

Bromine (Br)

Atomic Structures Can Be Represented by Symbols (nuclear symbols)

Each element has a name and symbol that is listed in the periodic table of elements.

Sometimes, atomic numbers and mass numbers are written with an element’s symbol.

Atomic #: whole numberMass #: has decimal point

Atomic Structures Can Be Represented by Symbols

The atomic number always appears on the lower left side of the element’s symbol:

1H 2He 3Li 4Be 5B

Mass numbers are written on the upper left side of the symbol:

11H 2

4He 37Li 4

9Be 511B

**mass number = protons + neutrons**

Isotopes of an Element Have the Same Atomic Number

All atoms of an element have the same atomic number and the same number of protons.

However, atoms of the same element do not necessarily have the same number of neutrons.

Isotope: an atom that has the same number of protons (atomic number) as other atoms of the same element, but has a different number of neutrons (atomic mass).

Two Ways of Identifying Isotopes1. Write the mass number with a hyphen after the

symbol for the element:He-3

This is a helium atom with a mass number of 3.

2. Write the nuclear symbol for the isotope:

23He

This is also a helium atom with a mass number of 3.

*Remember: all isotopes of an element have the same atomic number and the

same number of protons!*

Sample Problem B, pg. 89Calculate the number of protons, electrons, and

neutrons in oxygen-17 and in oxygen-18.These are both isotopes of oxygen, whose atomic

number is 8.Atomic number = number of protons = 8Protons = electrons = 8Mass number = proton + neutronsFor oxygen-17: 17 = 8 + neutrons

Neutrons = 9For oxygen-18: 18 = 8 + neutrons

Neutrons = 10

Movie: “Writing Nuclear Symbols”The movie is really short, about 8 minutes.

WorksheetComplete the front side of the worksheet

that goes along with the movieThe back side is homework

HomeworkSection 3.2 review, pg. 89: #1-8Finish “Writing Nuclear Symbols” worksheetConcept Review: “Structure of Atoms”

*Be ready for a quiz over section 3.2 next time*