Friday, Oct. 25 th : “A” Day Monday, Oct. 28 th : “B” Day Agenda  Finish section 3.2: “Structure of Atoms” Atomic number, mass number, isotope  Movie: “Writing Nuclear Symbols” and worksheet  Homework: Sec. 3.2 review, pg. 89: #1-8 Finish movie worksheet Concept 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. 86  How 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 = 29 Protons = electrons = 29 Mass number = protons + neutrons 64 = 29 + Neutrons Neutrons = 35

Practice Problem #3, pg. 86  Calculate the mass number for an atom that has 45 neutrons and 35 electrons. Mass number = protons + neutrons Protons = electrons = 35 Mass number = Mass number = 80  Which 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 number Mass #: 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: 1 H 2 He 3 Li 4 Be 5 B  Mass numbers are written on the upper left side of the symbol: 1 1 H 2 4 He 3 7 Li 4 9 Be 5 11 B **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 Isotopes 1.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: 2 3 He 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. 89  Calculate 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 = 8 Protons = electrons = 8 Mass number = proton + neutrons For oxygen-17: 17 = 8 + neutrons Neutrons = 9 For oxygen-18: 18 = 8 + neutrons Neutrons = 10

Movie: “Writing Nuclear Symbols”  The movie is really short, about 8 minutes.  Worksheet Complete the front side of the worksheet that goes along with the movie The back side is homework

Homework  Section 3.2 review, pg. 89: #1-8  Finish “Writing Nuclear Symbols” worksheet  Concept Review: “Structure of Atoms ” *Be ready for a quiz over section 3.2 next time*