Elements are made of atoms = the smallest particle that has all the characteristics of the element

How Small is an Atom?

•A copper penny contains 2.4 x 1022 atoms

•Earth’s population is approx. 7 x 109

•A scanning tunneling microscope makes it possible to see individual atoms

•TED

Scanning Tunneling Microscope

Atom Image

Subatomic Particles

•Mass of atom is generally protons + neutrons, majority of mass is in nucleus

•Mass of proton = 1•Mass of neutron = 1•Mass of electron = 1/2000

•(mass of H proton = 1 = is standard)

Subatomic Particles

Subatomic Particle

Charge Location

Proton

Neutron

Electron

Why?

Distinguishing Between Atoms

Atomic Number (Z)

•Found on the periodic table

•Is equal to the number of protons

•Each element has its own atomic #

•# protons = # electrons

Average Atomic Mass

•Also found on the periodic table

•Is the average mass of all of the atoms of that element

•Mass number = (A) actual mass of one atom

•Mass number = protons + neutrons

Carbon-12?

When written in this format…12 is the mass #

Practice with a Partner

Atom Symbol

Atomic #

Aver Atomic Mass

Mass # #

protons

# neutrons

# electrons

Lithium 7

Boron 9

Carbon 12

Nitrogen 14

Oxygen 16

Helium 4

Sodium 23

Isotopes

•Atoms of the same element that have different masses

•Have different masses because they have different numbers of neutrons

•# protons always the same

Example

•Carbon isotopes▫ Carbon-12▫ Carbon-13▫ Carbon-14

•Might also be written C-12, C-13, C-14

•Or

Nuclear Formulas

•Used to write isotopes…

Isotopes

•How are isotopes similar?

•How do they differ?

•Isotopes are chemically alike b/c they have identical numbers of protons & electrons

Average Atomic Mass

•How is it calculated?

•Based on the relative abundance of the naturally occurring isotopes of the element

•Each isotope has a fixed mass and a natural % abundance

Question

•With the following information, calculate the average atomic mass of chlorine:

▫76% of chlorine isotopes found naturally have a mass of 35

▫24% of chlorine isotopes found naturally have a mass of 37

Warm Up 1/15/2014

•P. 85 2-3•P. 87 6-9

•Calculate average atomic mass given the following information:

▫Carbon-12 is found naturally 98.89% of the time

▫Carbon-13 is found naturally 1.11% of the time

Warm Up1/16/2014•Write the procedure for determining

average atomic mass (paragraph format, complete sentences).

•Quiz tomorrow—cumulative

•Homework tonight

Atomic Theories

•Democritus•John Dalton•JJ Thomson •Ernest Rutherford •Niels Bohr•Schrodinger

“Atom” & Democritus

•400 BC

•Called nature’s basic particle an atom

•Atom (Greek) means uncuttable or indivisible

•No experimental evidence

Dalton’s Atomic Theory (1808)▫All matter is composed of tiny indivisible

particles called atoms▫Atoms of the same element are identical▫Atoms of different elements can physically mix

together or can chemically combine with one another in simple whole number ratios to form compounds

▫Chemical reactions occur when atoms (in compounds) are separated, joined, or rearranged

Dalton’s Atomic Theory

•Much of Dalton’s theory is accepted …except ?

•Except that atoms are indivisible AND that all atoms of an element are identical

Thomson & Plum Pudding Model•1897

•Discovered the electron

•His model proposed that negatively charged particles were randomly distributed within a pudding of positively charged particles

Rutherford & The Gold Foil

•1909

•Discovered the atom’s nucleus

•He bombarded a thin, gold foil with fast moving alpha particles (p 72-73)

Rutherford & The Gold Foil• A small amount of particles were deflected by

the tiny nucleus; most of the particles passed on through

• He concluded the volume of the atom was mostly empty space

Bohr’s Atomic Model• 1915

• Electrons organized in energy levels or shells around a nucleus of protons and neutrons

• A “planetary” model—not entirely correct

The Electron Cloud & Schrodinger• Is a probability model

• Describes a cloud like region where the electron is likely to be

• Based on mathematical equation

Project Time

A Closer Look…the Bohr Model Video

Bohr’s Model of the Atom • Scientists found that when an electric current is

passed through a glass tube that contains hydrogen gas, the tube emits light

• When this light is passed through a prism, four narrow bands of bright light are observed against a black background

• This is hydrogen’s line emission spectrum• Bands are at specific wavelengths, which are

unique to each element

Niels Bohr

•Niels Bohr proposed a model for the hydrogen atom that explained the spectrum of the hydrogen atom.

•The Bohr model was based on the following assumptions:

Bohr’s Model of the Hydrogen Atom

▫Electrons are arranged in concentric circular paths or orbits around the nucleus

▫Electrons in a particular path have a fixed energy

▫The energy of the electron in an orbit is proportional to its distance from the nucleus. The further the electron is from the nucleus, the more energy it has.

▫An electron can either gain or lose energy inside this orbit, electrons can move up or down to another orbit

Continued…• A quantum of energy = is the amount of energy

required to move an electron from its present energy level to the next higher one

• Light is absorbed when an electron jumps to a higher energy orbit and emitted when an electron falls into a lower energy orbit

Continued…• The energy of the light emitted or absorbed is

exactly equal to the difference between the energies of the orbits

• The energy given off is electromagnetic radiation

• Is given off as photons (particle of light with no mass)

Continued…

•Lowest energy state of atom = ground state

•Higher energy state of atom = excited state

•Neon signs—excited neon atoms emit light when falling back to the ground state

Project TimeReminder…Quiz tomorrow

Warm Up 1/17/2014

•How did Bohr’s model of the atom differ from Schrodinger’s?

Modern Atomic Theory

Electron Cloud Model

•AKA quantum mechanical model

•Clouds of probability = where electrons are most likely to be

•Electrons are located in orbitals (not orbits)

Electron Cloud Model

•4 types of orbitals: s, p, d, f

•Each orbital can only hold 2 electrons

Warm Up 1/21/2014

•Construct a table to compare subatomic particles.

Warm Up1/24/2014•Create a Venn diagram to compare the

Bohr model to the electron cloud model.

•Homework DUE

•Quiz today

Warm Up1/27/2014•Given an isotope for fluorine, fluorine-

19…

•What is Z?•What is A?

Quizzes

•Dropped one question

•2nd block 84

•3rd block 86

What are ions?Why would ions form?Atoms with a chargeWhen they gain, lose, or share electronsBut…why would they do this?

What is the Octet Rule?Says that atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell…More specifically, the number of electrons needed to fill the s and p sublevels of that energy level

Practice

Nuclear Chemistry

How Atoms CombineSection 3.2

Chemical Properties

•Chemical properties = how reactive an atom is

•Does it like to combine with other atoms or is it stable alone?

•Which groups on the periodic table are reactive?

•Which groups are stable?

Compounds

•A substance that is composed of atoms of 2 or more different elements that are chemically combined

•Example = NaCl

•Why do these two atoms like to combine? (draw)

Types of Bonds

• Ionic bonds—when atoms lose or gain electrons

•Example = _____________

•Covalent bonds—when atoms share electrons

•Example = ______________ (draw)

Compounds

•Atoms want their outer energy level filled with electrons, in most cases this is 8 electrons

•Which groups on the periodic table would you predict would commonly form bonds together?

•Class Bonding Activity

Warm Up8/30/12Complete Section Assessment 3.1 #1-5 on page 59

Group Assignment

•Chemical Reactivity worksheet

Independent Notebook Assignment•Vocabulary section 3.2 (page 60)

Independent Assignment

•Create a poster—to display a large drawing of an atom…the element will be assigned to you.

•Format: see example

•Grading: based on neatness & accuracy.

Element Assignment

Warm Up8/31/12What group # is chlorine in?What is its symbol?List everything that you can learn about chlorine based its location in the periodic table. Include what other elements it might bond with.

Agenda

•Quiz

•Project Presentations