Chemistry

Mr. McCalla“Mack”Rm 230

Class Rules

• If your not in your seat by the second bell, you’re late…..!

• All assignments must be handed in on time. Late submissions will NOT be accepted.

• When I speak……YOUR MOUTH STOPS WORKING……..!

• Expect nightly homework, a weekly quiz on Wednesdays and exams on Fridays.

What do I need for this class…?

Out side of the usual supplies (pens, paper),you are required to have the following:

1. 3-ringed binder.2. 2-3 folders for the 3-ringed binder.3. A spiraled notebook with 3-ringed holes for the

binder.*You will be graded on the contents of your binder so

always make sure it is in order with notes, handouts, returned papers, quizzes and exams*

What is Chemistry?

• Chemistry: the study of matter, which is anything that has mass and volume.– Your desk your sitting on, the air around you, and

your body are all made up of matter.– Everything is composed of Atoms– Chemistry deals with the composition of matter

and the changes that matter may undergo.• Water - Ice – Vapor

Early Studies of Atoms

The Greeks were the first to take a closer lookat the physical world around them. They concluded that is composed of fire, air, waterand earth.

A scientist by the name of Robert Boyle identifiedGold and Silver as elemental; that is, they are not themselves made of fire, air water and earth causing the Greek concept to fade.

Robert Boyle

Dalton’s Atomic Theory

• The work of Boyle led a scientist by the name of John Dalton to propose his revolutionary theory in the 1700s.

• He theorized that the basic unit of matter is a tiny particle called an atom.

• Dalton’s theory of the atom can be summarized by the following points:

John Dalton

Dalton’s Atomic Theory

1. All elements are composed of indivisible atoms.

2. All atoms of a given element are identical.3. Atoms of different elements are different;

that they have different masses.4. Compounds are formed by the combination

of atoms of different elements

Structure of the Atom• J.J. Thompson was one of the

first scientist to identify the smaller units that made up an atom.

• He used a cathode ray tube and gold foil to show one of these smaller units (electrons) that make up the atom

J.J. Thompson

• A concept of the atom developed in which these negatively charged particles are visible like raisins in bread. This model called the “plum model”; the mass of the rest of the atom was distributed and positively charged, taking space not used by the electrons.

• Because the ray produced by in the tube was deflected by the gold foil a certain way by an electrical or magnetic field, he concluded that the ray was formed by negatively charged particles.

• These negatively charged particles are called electrons.

Structure of the Atom• Earnest Rutherford led a group

of scientist that directed alpha particles (positive) at a piece of gold foil.

• Most of the particles passed straight through the foil.

• To their surprise some of the alpha particles where greatly deflected and some bounced back.

Earnest Rutherfod

Structure of Atoms

• Rutherford concluded that atoms have a dense central core, called the Nucleus, while the remainder of the atom is essential empty space.

• Because alpha particles are positively charged and were repelled by the nucleus, the nucleus must be positively charged because like charges repel each other.

Modern Atomic Theory

• The Bohr Model of the Atom: In the early 20th century the common model of the atom was the Bohr or “planetary model”.

• The model showed a center nucleus (protons and neutrons) and rings with orbiting electrons.

• The outer most electrons (electrons that are in the last orbital are called valence electrons.

Modern Atomic Theory

• The Wave-Mechanical Model: Modern advancements in the study of energy aided in the modifying of the atomic model.

• This model of the atom pictures the atom as having a dense, positively charged nucleus as proposed to the planetary model .

• The major difference between the wave-mechanical model and the Bohr model is found in which manor the electrons are pictures.

Modern Atomic Theory

• Instead of moving in definite, fixed orbits around a nucleus as suggested in the Bohr model, the wave-mechanical model portrays electrons with distinct amounts of energy moving in areas called orbitals.

• Orbital: a region in which an electron of a particular amount of energy is most likely to be located .

The Wave Mechanical Model

• Energy and matter were viewed as both waves and particles.

• Energy was made up of tiny packets called quanta which acted like particles.

• This model pictures the atom as having a dense, positively charged nucleus as proposed in the planetary model.

Atomic Number• Atomic Number = the number of

protons/electrons• Atomic Mass = protons + neutrons.• Atomic Symbol = symbol for the element

Isotopes

• Isotopes are atoms of the same element that have different number of neutrons, hence have a different mass number

Isotope Symbols

• Isotopes can be identified by using a symbol the indicates both the element and its mass number.

• Thus C-12 represents a carbon atom with the mass number of 12 which represents the sum of the protons and neutrons.

• Because the atomic number of C-12 is 6, the number of neutrons will also be 6.

Subatomic Particles

• Protons have a mass of only 1.67 x 10• Because the mass of a proton is so small, it is

more convenient to use a different scale called atomic mass units.

-24

Location of Electrons

• Remember that electrons are found in the space of the atom around the nucleus.

• Experiments have shown that electrons are in orbitals.

Energy Levels

• The orbital in a atom form a series of energy levels in which the electrons can be found.

• Each electron in an atom has its own distinct amount of energy that corresponds to the energy level that it occupies.

• Electron can gain or lose energy and move to different energy levels.

How to calculate AMU

• How to calculate AMU – Atomic Mass Units• Atomic mass units can be calculated from the

mass and the abundance of naturally occurring isotopes.

• Carbon has two naturally occurring isotopes.

98.89% C-121.108% C-13

1. Convert the percentages to decimal numbers, and multiply the mass of each isotopes by its decimal abundance

12 amu x 0.9889 = 11.87 amu13 amu x 0.01108 = 0.1440

• 2. Add these masses of isotopes. 11.87 amu + 0.1440 amu = 12.01

amu

• Naturally occurring europium (Eu) consists of two isotopes was a mass of 151 and 153. Europium-151 has an abundance of 48.03% and Europium-153 has an abundance of 51.97%. What is the atomic mass of europium?

Subatomic Particles

Masses

• Mass of the electron= 1/1836 amu of a proton

• 1 amu = 1.7 x 10 -24

Isotopes of Hydrogen

• Protium: P:1 N:0 Mass Number: 1 amu

• Deuterium: P:1 N:1 Mass Number: 2 amu

• Tritium: P:1 N:2 Mass Number: 3 amu

Orbits in Detail

• Electrons are found in the space of the atom around the nucleus.

• Orbitals in an atom form a series of energy levels in which electrons may be found

• Each electron atom has its own distinct amount of energy that corresponds to the energy level.

Orbits in Detail

• Electrons can gain or lose energy and move to different energy levels, but they do so in a unique way.

• If an electron moves from one energy level to another, it must give off or absorb the energy difference between the two levels

Ground and Excited States

• When electrons occupy the lowest available orbital, the atom is said to be in the ground state.