The Structure of Atoms Thanks to those 7 scientists (and many more) what do we know about atoms today?!

Structure of atoms Atoms can’t be broken into smaller pieces, BUT they are made of smaller pieces! Those smaller pieces all on their own don’t act like the element the atom is from. Atom: the smallest particle of an element with the chemical properties of that element.

Two areas of an Atom Nucleus: made up of: Protons (+ positive), mass number = 1 Neutrons (0 neutral), mass number = 1 Make up the mass of the atom +

Electrons (- negative) Around the nucleus Tiny, mass number = 0 Lots of space between the nucleus and the electrons. -

Subatomic Particles Protons, neutrons and electrons

Subatomic Particles Subatomic Particle Charge Location Mass proton positive (+) nucleus 1 amu neutron neutral (0) electron negative (-) around nucleus ~1/2000 amu

Defining an Atom Nuclei (plural of nucleus) made of protons and neutrons Number of Protons (+) = number of electrons (-) Atoms are neutral! # protons tells us what kind of element an atom is!

Holding it all together Nuclear forces hold protons and neutrons together The positive force of the nucleus holds the electrons near the nucleus. Positive and negative attract.

Mass number = protons + neutrons Everything heavy in an atom Electrons aren’t heavy at all!

C 6 Carbon 12.011 Atomic Number (= number of protons) Element Symbol Element Name Average atomic mass

Protons Neutrons Mass number Electrons Element

+ -

Protons Neutrons Mass number Electrons Element 2 4 Helium

- + + + - -

+ - +

- - - + + - + + - + + + - -

- - - + + + + - + + - + + + + - - - - -

- - - + - + + + - + + - + + + + + - - - - -

- - - + + + - + + - + + + - - -

2 4 Helium 3 6 Lithium 5 10 Boron 7 14 Nitrogen 20 Neon 11 22 Sodium 8 Protons Neutrons Mass number Electrons Element 2 4 Helium 3 6 Lithium 5 10 Boron 7 14 Nitrogen 20 Neon 11 22 Sodium 8 16 Oxygen

Which element…? Has 20 protons?

Which element…? Has 15 protons?

Which element…? Has 17 protons?

Which element…? Has 53 protons?

Which element…? Has 79 protons?

Which element…? Has 40 electrons?

Which element…? Has 77 electrons?

Which element…? Has 50 electrons?

Which element…? Has 118 electrons?

C 6 Carbon 12.011 Atomic Number (= number of protons) Element Symbol Element Name Average atomic mass

Protons: defining an atom Atomic number: Atoms of different elements have different numbers of protons.

Trends in Atomic Numbers Atomic numbers increase to the right and down the Periodic Table of the Elements. Check it out.

Isotopes

Average atomic mass + - 6 C 12.01 + + -

But why is the atomic mass (on the periodic table) different from the mass number (protons + neutrons)? Carbon atomic mass = 12.011 amu Mass number = 12 amu

Isotopes Atoms of the same element can have different numbers of neutrons. Because these atoms have the same number of protons, they are the same element, and acts the same More or fewer neutrons only changes the mass of the atom! Isotopes are atoms of the same element with different masses because of different numbers of neutrons Identified by mass number

Naming Isotopes Mass number (A): the total number of protons and neutrons in the nucleus of an isotope Hyphen Notation: Element-Mass number Hydrogen-3

Nuclear Symbol

Nuclear symbols Helium-4: 4 is the mass number The total number of protons plus neutrons This helium isotope can also be written: 4He 2 4 is the mass number, 2 is the number of protons Write the nuclear symbol for Carbon-13 13C 6

Nuclear symbols Helium-4: 4 is the mass number The total number of protons plus neutrons This helium isotope can also be written: 4 is the mass number, 2 is the number of protons (from the periodic table)

Isotope Notation Mass number Atomic number Al-27 Aluminum-27

+ -

- +

- + + -

+ - +

- - + - + + + + - -

- - - + + - + + - + + + - -

- - - + + - + + - + + + - -

- - + + - - + + + + - -

+ - +

- - + - + + + + - -

- - - + + - + + - + + + - -

- - - + + - + + - + + + - -

Practice naming Isotopes The notation Sn-117 represents an isotope of the element ____________. Its mass number is ________. Since its atomic number is __________, the atom contains _________ protons, _________ electrons and _________ neutrons.

Cesium-133 is an isotope whose mass number is _________. Its atomic number is ________. The atom contains _______ protons, ________ electrons and ________ neutrons.

An isotope contains 27 protons and 39 neutrons An isotope contains 27 protons and 39 neutrons. The isotope is an atom of the element ____________. Its atomic number is _________. This atom has _______ electrons. Its mass number is __________.

Applications of Isotopes Over time (a long time!) one isotope can lose neutrons and turn into another.

Measure the % of C-14 to calculate age

What objects have been dated using carbon-14 isotopes?

Shroud of Turin

The Giant Periodic Table Project 6 C Carbon 12.011

The Giant Periodic Table Project Be neat Be bold! We need to be able to read this from anywhere in the room! Be creative, but not cluttered. Be accurate. Atomic mass to TWO digits (Ex: 12.01) is ideal.

Calculating your grade Your averages for each of the categories are: Tests: 79% Labs: 88% Homework: 65% Class work: 90% Let’s imagine that your grade in biology was based on the following: 40% Tests 30% Labs 20% Homework 10% Class work

Now you try: Your averages for each of the categories are: Tests: 90% Labs: 70% Homework: 85% Class work: 95% Let’s imagine that your grade in biology was based on the following: 40% Tests 30% Labs 20% Homework 10% Class work

Mixtures of Isotopes In nature, elements occur as a mixture of isotopes. We use the weighted average of the isotope masses – average atomic mass On the periodic table, the average atomic mass is below the element name. Check it out.

Example: Chlorine In nature, chlorine exists as: 75.77% chlorine-35

In nature, the element lithium has isotopes in the following natural abundance: Calculate the average atomic mass.

Copper has two naturally occurring isotopes Copper has two naturally occurring isotopes. They are present in the following percents: 69.09% 30.91 Calculate the average atomic mass.

Calculate the average atomic mass of Ne

So what if someone gives us the mass of a sample of an element? How do we figure out how many atoms we have? We use… THE MOLE

The mole Mole: The SI unit for amount of substance Contains as many particles as there are atoms in 12 grams of carbon-12 There are 6.022x1023 atoms in 12 grams of carbon-12 Avogadro’s Number = 6.023x1023

Molar Mass The mole: the amount of a substance that contains one Avogadro’s number (that is, 6.022x1023) of particles. Molar mass is the mass of one mole of a pure substance (units: g/mol)

Find the molar mass of… Oxygen

Find the molar mass of… Phosphorus

Find the molar mass of… Sodium

Find the molar mass of… Gold