3.1MATTER, ENERGY, AND

EARTH CHEMISTRY

PROPERTIES OF MATTER Matter is anything taking up space and having mass.

The amount of matter in an object is its mass.

3 main states of matter include: SOLID: definite mass, definite volume, definite shape LIQUID: definite mass, definite volume, indefinite shape GAS: indefinite mass, indefinite volume, indefinite shape

The amount of disorder in atoms or molecules is known as entropy. Example: SOLID LIQUID = Entropy increasing Example: GAS SOLID = Entropy decreasing

PROPERTIES OF MATTER All matter has 2 types of distinguishing

characteristics: Physical properties Chemical properties

Physical properties can be observed without changing the composition of the substance. Examples: density, color, hardness, freezing

point, boiling point, and the ability to conduct electricity.

Chemical properties describe how a substance reacts with other substances. Examples: oxidation (iron reacting with oxygen

to form rust).

PROPERTIES OF MATTER An element is a substance that cannot be

broken down into simpler, stable substances by ordinary chemical means. About 90 elements occur naturally on Earth. 8 of those make up more than 98% of Earth’s crust.

Elements consist of atoms, which are the smallest units of an element having the chemical properties of that element. A single atom is so small, its size is difficult to

imagine. Look at the thickness of a sheet of notebook paper

about 1,000,000 atoms lined up side by side would be equal to that thickness.

ATOMIC STRUCTURE Atoms are made up of even smaller

parts called subatomic particles.

3 major kinds include: Protons – subatomic particle having a

positive charge located in the nucleus of an atom.

Neutrons – subatomic particle having no charge located in the nucleus of an atom.

Electrons – subatomic particle having a negative charge located in energy levels surrounding the nucleus of an atom.

ATOMIC STRUCTURE The maximum number of electrons an energy level can

occupy is expressed by the formula 2n2, where n= the energy level.

TRY THE FOLLOWING … Oxygen (O) Magneisum (Mg)

8 protons, 8 neutrons, 8 electrons 12 protons, 12 neutrons, 12 electrons

ATOMIC NUMBER The number of protons in the nucleus of an

atom is called the atomic number. All atoms of any given element have the same

atomic number thus the same number of protons.

Since an uncharged atom has an equal number of protons and electrons, the atomic umber is also equal to the number of electrons.

THE PERIODIC TABLE OF ELEMENTS The Periodic Table of Elements is a

system for classifying elements and was first devised by the Russian chemist, Dmitri Mendeleev, in 1869.

Elements on the Periodic Table are ordered according to their atomic numbers. Rows are called periods. Columns are called groups.

Elements in the same column have similar arrangements of electrons around their atom, therefore having similar chemical properties.

Mendeleev

MASS NUMBER The sum of the number of protons

and neutrons in an atom is the mass number. This is the atomic mass rounded to

the nearest whole number.

The mass of a subatomic particle is too small to be expressed in grams. So, we use a special unit called the

atomic mass unit (amu). Protons and neutrons each have an

atomic mass close to 1 amu. In contrast, electrons have much less.

The mass of 1 proton is equal to the combined mass of about 1840 electrons!

ISOTOPES Although atoms of a given element contain the same number of

protons, the number of neutrons may differ.

An atom of the same element having the same number of protons (atomic number), but a different number of neutrons (different mass number) is called an isotope.

ISOTOPES A Carbon-14 atom having 8 neutrons is more massive than a Carbon-11

atom having only 5 neutrons. Different isotopes of the same element have slightly different properties.

Unstable isotopes are subject to radioactive decay, where they will emit energy and change into another element.

Since isotopes of an element have different masses, the Periodic Table uses an average atomic mass, which is the weighted average of the atomic masses of the naturally occurring isotopes. Isotopes of Hydrogen (H): 1H, 2H (Deuterium), and 3H (Tritium).

On the Periodic Table, the average atomic mass of Hydrogen (H) is 1.00794 u.

VALENCE ELECTRONS An atom’s chemical properties are largely determined by the number of

the outermost electrons, valence electrons, in an atom’s electron cloud. Within each group (column), the atoms of each element generally have the

same number of valence electrons. For Groups 1 and 2, the number of valence electrons in each atom is the same

as that atom’s group number. Atoms of elements in Groups 3-12 (Transition Metals) have 2 or more valence

electrons. For Groups 13-18, the number of valence electrons in each atom is the same as

that atom’s group number minus 10, except for Helium (He), which only has 2 valence electrons.

PERIODIC PROPERTIES Elements whose atoms have only 1, 2, or 3 valence

electrons tend to lose electrons rather easily. These elements have metallic properties and are

generally classified as metals.

Elements whose atoms have from 4-7 valence electrons are more likely to gain electrons. Many of these elements are classified as nonmetals.

When an atom has 8 valence electrons, it is considered stable, or chemically un-reactive. It’s outer shell is full … Octet Rule

COMBINATIONS OF ATOMS Elements rarely occur in pure form in Earth’s crust, but

rather as a combination with other elements we discussed Quartz, SiO2

A substance made of two or more elements chemically combined is called a compound.

A group of atoms held together by chemical forces is called a molecule. All compounds are molecules, but not all molecules are compounds!

Some elements occur as diatomic molecules, which are molecules made up of only two atoms.

Mnemonic: I Have No Bright Or Clever Friends Iodine (I2), Hydrogen (H2), Nitrogen (N2), Bromine (Br2), Oxygen (02),

Chlorine (Cl2), and Fluorine (F2).

COMBINATIONS OF ATOMS

CHEMICAL FORMULAS A chemical formula is a combination of letters and

numbers showing which elements make up a compound. Also shows the number of atoms of each element that are

required to make a molecule of a compound.

The chemical formula for water is H20, indicating each water molecule consists of 2 atoms of Hydrogen and 1 atom of Oxygen, shown by the subscript.

x2 x2Superscript

Subscript

CHEMICAL FORMULAS Another example of a chemical formula is sodium

chloride, NaCl, halite, or table salt … they all mean the same thing! Sodium (Na) is a silvery metal and Chlorine (Cl) is a

poisonous greenish-yellow gas. They both make up table salt, which you can eat.

+ =

CHEMICAL EQUATIONS A chemical reaction showing the combination

of elements and compounds is called a chemical equation. The reactants are on the left-hand side of the

arrow, combining to form the products, on the right-hand side of the arrow. The arrow means “yields” or “gives”.

CHEMICAL EQUATIONS Chemical equations must be balanced to show

accurate chemical information. An equation is balanced when the number of atoms of

each element on the right side equal the number of atoms of the same element on the left side.

You cannot change the chemical formulas, but rather put numbers called coefficients in front of chemical formulas. A coefficient multiplies the subscript in a formula; 4

Hydrogen (H) atoms are in the formula 2H20.

CHEMICAL EQUATIONS Try balancing the following equations:

___ Hg + ___ O2 ___ HgO

___ KNO2 + ___ O2 ___ KNO3

___ Al + ___ HCl ___ AlCl3 + ___ H2

Easy Stuff!

2 1 2

22 1

6 22 3

CHEMICAL BONDING The forces holding the atoms in

molecules together are called chemical bonds. They form due to the attraction between

positive and negative charges.

Atoms form chemical bonds by either transferring or sharing valence electrons from one atom to another. When this happens, the atoms become

charged.

A particle, such as an atom or molecule, carrying a charge is called an ion.

CHEMICAL BONDING An attraction between oppositely charged ions

resulting in the transfer of electrons from one atom to another is called an ionic bond.

CHEMICAL BONDING Let’s look again at NaCl, or sodium chloride:

CHEMICAL BONDING The Sodium (Na) atom transfers 1 electron, becoming

positively charged (Na+1). The Chlorine (Cl) atom accepts the 1 electron, becoming

negatively charged (Cl-1). This chemical reaction results in table salt, NaCl.

CHEMICAL BONDING An attraction between atoms sharing electrons is

called a covalent bond. The positive nucleus of each atom is attracted to the

shared negative electrons.

MIXTURES On Earth, elements and compounds are

generally mixed together. A mixture is a combination of 2 or more

substances not chemically combined.

Mixtures in which 2 or more substances are not uniformly distributed are called heterogeneous mixtures. Examples include: igneous rock, granite (contains

the minerals quartz, feldspar, hornblende, and biotite mica).

Mixtures in which 2 or more substances are uniformly dispersed throughout are called homogeneous mixtures. Examples include: Sea water (NaCl is dissolved in

H2O).