Chapter 3

Elements

Periodic Table

Compounds

Elements

All words in the English language are the result of the 26 letters of the alphabet.

All substances on our planet and the universe are the result of about 88 known “building blocks” called the elements.

Why 88?

Elements

An element cannot be decomposed into a simpler substance.

The smallest particle of an element is the atom.

Atoms are incredibly small.

Elements

Every element has a one or two letter designation called its _____________.In writing a symbol, the first letter is capitalized and the second letter is lowercase.C = carbonCo = cobaltBut, CO = a compound of carbon and oxygen!

Distribution of the Elements

Most elements are solids at 25oC.Br and Hg are liquidsH, N, O, F, Cl, He, Ne, Ar, Kr, Xe, and Ra

are gases

Silicon and oxygen make up almost 75% of the Earth’s crust.

DistributionAbundancein Earth's

Crust

Others4.5%

Potassium2.4%

Calcium3.4%

Sodium2.6%

Iron4.7%

Aluminum7.5%

Silicon25.7%

Oxygen49.2%

History of the Elements

Some elements were known to ancient man like Copper and Gold.

Names and symbols are based in Latin language

Copper = Cuprum; symbol Cu

Gold = Aurum; symbol Au

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Common Elements

Aluminum Argon Arsenic Barium Boron

Bromine Calcium Carbon Chlorine Chromium

Cobalt Copper Fluorine Helium Hydrogen

Iodine Iron Lead Lithium Magnesium

Manganese Mercury Neon Nickel Nitrogen

Oxygen Phosphorus Potassium Silicon Silver

Sodium Strontium Sulfur Tin Titanium

Vanadium Zinc

Periodic Table

Dimitri Mendeleev, 1869

Elements are arranged into vertical columns called groups.Elements within the same group tend to

react in the same way.

Horizontal row = period.

Periodic Table

Main (representative) groups = A

Transition groups = B

Groups with special namesAlkali metal, alkaline earth metal,

halogens, and the noble gases.

Actinide and lathanides.

Periodic Table

A stair-step line on the right-hand side of the chart separates the metals from the non-metals.

Metals are solids, have luster (shine), are good conductors, are malleable,and are ductile. Most have a high density and high melting point.

Periodic Table

Non-metals are dull, are poor conductors, and have low melting points and densities.Metalloids are elements that fall on or near the line and have properties of both metals and non-metals.B, Si, Ge, As, Sb, Te, and Po

Hydrogen – a special exception.

Groups

Learning Check

Describe each in terms of a Group, Period, and Metal, non-metal, or metalloid.

Element Group Period M/NMMg

C

FeAs

Elements in Nature

Elements are rarely found in their pure form in nature.Exceptions are metals like Gold, Silver,

and Platinum; non-metals like Nitrogen and Oxygen; and the noble gases.

Most are combined with other elements as compounds.

Diatomics

Some important elements occur as two atoms bonded together.

The list is:

Compounds

Compounds are classified as either Molecular or Ionic.Molecular (aka covalent) compounds are

formed between two or more non-metals who share electrons.

Ionic compounds are formed between a cation (+) and an anion (-).

Compounds

Metals lose electrons and form cations.Na Na+1 + 1e-

Non-metals gain electrons and form anions.Cl + 1e- Cl-1

Thus, an ionic compound will have a metal and a non-metal in its formula.

Compounds

Law of Constant Composition – any sample of a compound will always have the same ratio or mass percentage of its elements.Water always has two hydrogen atoms and one oxygen atom per formula.Sodium chloride always has one sodium and one chlorine atom per formula.

Chemical Formulas

Are a shorthand method for writing names.

Subscripts indicate the number of each of the elements in the compound.

A subscript of one is NEVER written.

Ex) CO2, MgBr2, C6H12O6.

Learning Check

Decide whether the following would be a molecular or ionic compound.

Compound Type

MgBr2

SO2

FeCl3PF3

Chapter 5

Atomic Theory

Discovery of Atomic Structure

Subatomic Particles

Nuclear Atom

Dalton’s Model

1. All matter is made up of tiny particles called atoms.

2. All atoms of a given element are similar to one another; atoms of different elements are different from each other.

3. Atoms of two or more different elements combine to form compounds.

4. A chemical reaction involves the rearrangement of atoms into new combinations. Atoms are never created nor destroyed in a chemical reaction.

Parts of an Atom

Experiments performed around the turn of the previous century (~1900), showed that atoms were made of several types of particles – collectively referred to as subatomic particles.

These experiments showed that three types of particles were present in an atom.

Subatomic Particles

A proton has a +1 charge and an approximate mass of 1 amu.Note: an atomic mass unit (amu) is equal to 1/12 of the mass of a Carbon atom with 6 protons and 6 neutrons.A neutron has no charge, but does have a mass of about 1 amu.An electron has a –1 charge and a mass so small that we usually say that it weighs 0 amu.

Atomic Structure

Ernest Rutherford performed an experiment called the “Gold Foil” experiment in 1911.

He used an alpha particle (2P + 2N) source and fired them at a piece of very thin gold foil.

He expected all of the particles to pass straight through. However, some were deflected and some were even reflected backwards.

In Rutherford’s words, it was as if he had shot a cannonball at a piece of tissue paper and have it bounce backwards.

Gold Foil Experiment

Results

Only 1 in 8000 alpha particles is scattered.

Scattering occurs when an alpha particle encounters a gold nuclei.

A nucleus is very small and contains both the protons and the neutrons. Thus, it contains almost all of the mass of an atom.

This very dense center is surrounded by the electron cloud, which is occupied by the fast moving electrons.

Thus, an atom is MAINLY EMPTY SPACE.

Atomic Model

Atomic Number & Mass Number

All atoms of the same element have the same number of protons.

This distinguishes one element from another.

The number of protons is also called the atomic number.

This is always the integer found on the periodic chart with each chemical symbol.

Atomic Number & Mass Number

Atoms are electrically neutral. Thus, each element must have an equal number of protons and electrons.

The mass number of an atom is equal to the sum total of the protons and neutrons in the nucleus.

Mass number and atomic weight (found on the periodic chart) are NOT the same thing.

Study CheckName Symbol Atomic # Mass # #P #N #e

Carbon 12

N 8

26 30

Isotopes

All atoms of one element have the same number of protons.

But, they can have different numbers of neutrons, and hence, a different mass number.

These different versions of atoms from one element are called isotopes.

Isotopes

Use the chemical symbol, atomic number (Z), and mass number (A) as seen below.

Can also list symbol followed by mass number.

Atomic Mass

The masses found for each element on the periodic chart are the weighted average of all the known isotopes for that element.

Example: Chlorine has only two known isotopes – Cl-35 and Cl-37. Cl-35 is found 75.5% of the time and Cl-37 is found 24.5% of the time.

Isotope Mass X Percent = Contribution

(approximate) to total mass

35 amu X 0.755 = 26.4 amu

37 amu X 0.245 = 9.1 amu

Totals 1.000 35.5 amu

With all elements, round A.W.’s to one decimal place.

Study CheckWhat is the Atomic Weight of each element rounded to 0.1amu?NaSiClK