Unit 2 - Chapter 3Elements, Atoms,

Ions

The elements

•Can we name some?

•How many are there?

•Where would you find that information?

Element Symbols•Each element has a unique symbol.

•The first letter is always capitalized

•if a second letter, it is always lower case

•Usually the 1st letter of its name, then the 2nd letter or unique letter.

• Carbon, Calcium, Cadmium, Californium

•Some unusual symbols - mostly based on latin roots

• sodium, potassium, gold, lead, mercury, iron, etc.

Atomic size•We can take a chunk of matter and break

in apart into smaller and smaller pieces, eventually we would get down to individual atoms. Each piece would behave like the original chunk with all of its properties.

•The atom is the smallest particle of an element that retains the properties of the element.

•108 copper atoms lined up would be 1 cm. What would be the diameter of a single copper atom?

Atomic theory - Chpt 3.2

•Democritus (ancient greek philosopher) stated that if you broke down matter eventually you would get to the smallest particle of matter that could not be divided (atomos)

•John Dalton - 1800s - Did Chemical Experiments!

• Things (matter, compounds) always combined in the same proportions SIMPLE WHOLE NUMBER RATIOS

• Law of Constant Composition - a compound always has the same composition regardless of where it comes from or how it is made

• Dalton’s Atomic Theory - page 56 of textbook

Dalton’s Atomic Theory pg. 56 Textbook

•Elements are made of tiny particles - atoms

•All atoms of an element are identical.

•Atoms of an element are different from all other elements.

•Atoms can combined to form compounds. A compound always has the same number and types of atoms. SIMPLE WHOLE NUMBER RATIOS

•Atoms are not created nor destroyed by chemical reactions, simply rearranged or grouped together differently

Compounds• Compound is a distinct substance, that is

composed of 2 or more elements, always in the same proportions (whole number ratios)

• Can we name some?

• A compound has a unique chemical formula, which indicates which elements and how many are in that particular substance.

Atomic Structure - Chpt 3.3

• What is a Model of the atom?

• How did we get there?

• Dalton - Chemical Experiments determined atom was indivisible (a solid sphere)

• Cathode Ray tube experiments by J.J. Thomson (plum pudding model or TODAY maybe chocolate chip ice cream)

• Gold foil experiment by E. Rutherford (nuclear atom - the marble in the Metrodome)

J.J. Thomson’s Experiment• The cathode ray tube discovered was a beam of

particles

• The beam was deflected by magnets

• changed the gas -> didn’t change beam,

• changed metal anode -> didn’t change beam

• Particle was a fundamental particle of all substances!

• Particle was a part of all atoms!!!! 1st Subatomic particle, so the atom was made of smaller particles

• JJ Thomsom discovered the electron. Didn’t know about the rest of the atom, so just said it was like Plum Pudding

JJ Thomson experiment

Rutherford’s Gold foil

Experiment•Bombarded a thin gold foil with positively

charged alpha particles. Looked at flashes of light when film was hit.

•Most of the particles went straight through

•1 out of 20,000 bounced almost directly back

•Conclusions:

•Atom is mostly empty space

•positively charged nucleus with most of the mass

Rutherford’s Experiment

Isotopes• Not all atoms of an element are the same!

• The identity of an atom is determined by the number of protons.

• Atomic number is the # of protons in an atom, Z.

• atomic number is found on periodic table!

• # of protons = # of electrons in neutral atom.

• Mass number is the sum of the protons + neutrons in the nucleus of the atom, A

• #of neutrons = Mass number - Atomic number = A - Z

• Isotopes are atoms of the same element with different numbers of neutrons

Isotope examples• For the masses of atoms we use amu

(atomic mass unit) - 1 amu is defined as one-twelfth the mass of the carbon-12 atom.

• hydrogen-1, hydrogen-2, hydrogen-3

• also written 1H 2H 3H AH

• the number is the mass number, the atom name tells us how many protons!

• how many protons does hydrogen have?

• how many neutrons does each isotope have?

• oxygen-16, oxygen-17, oxygen-18

• how many protons and neutrons?

Atomic Mass•Atomic mass from periodic table is

a weighted average of the stable isotopes found on earth.

•If we are given the percentage of each isotope and its mass can calculate the atomic mass.

•Simply multiply the percentage times the mass for each isotope and add up each isotopes contribution to get the atomic mass.

Periodic Table - Chpt 3.4

• Write the key terms (pg. 68) in your notebook.

• The elements were organized into the Periodic Table by Mendeleev in 1869.

• Columns (groups or families) of elements have similar chemical properties

• He left blank spaces -

• prediction of previously unknown elements

• These were found and confirmed his predictions!!

• 7 periods (rows) , 18 groups (columns)

• alkali metals, alkaline earth metals, halogens, noble gases

Mendeleev’s 1869 Periodic Table

Properties of metals

•Solid, shiny

•Conduct electricity

•Conduct heat

•Malleable (hammer into shapes) and Ductile (drawn into wires)

Types of elements•Metals

•Non-metals

•Metalloids (semimetals) - along the staircase - separates the metals from the nonmetals

•Most elements are considered single atoms, a few are only found as diatomics - two atoms together, H2, N2, O2, F2, Cl2, Br2, I2

•hockey stick and puck or

•BrINClHOF “brinklehof”

Extra Credit - Unit 2

•Chapter 3 - pg. 86-88 , # 5, 6, 7, 10, 12, 14, 17, 18, 19, 21, 23, 29, 30, 33, 35, 39, 40, 41, 42, 46, 53, 55