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Earth Chemistry
Ch. 4 Notes
Ch. 4 S. 1
Matter
What about Mendeleev’s work makes
him stand out among other scientists of
his time? How was his work unique
when compared to others who were
doing similar research?
Properties of Matter

Matter – Anything that takes up space and has mass.

Two types of distinguishing characteristics:
 Physical
Properties – can be observed without changing the chemical
composition of the substance.
 EX:
Color, Shape, Boiling Point, Melting Point, Malleability, luster, state
of matter, scent, size
 Chemical
Properties – Describe how a substance reacts with other
substances.
 Ex:
how or if a substance reacts with water, or an acid, or oxygen.
http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/75013.h
tm
Write down some Physical Properties
of the object
Baking Soda Properties
Sort the properties into Chemical and Physical
properties
Properties list
Reacts with vinegar to produce
CO2
White solid powder
Not Flammable
Decomposed by acids
Tastes salty
Density = 2.20 g/cm3
Odorless
Chemical
Physical
Baking Soda Properties
Sort the properties into Chemical and Physical
properties
Properties list
Chemical
Physical
Reacts with vinegar to produce
CO2
White solid powder
Not Flammable
Decomposed by acids
Tastes salty
Density = 2.20 g/cm3
Odorless
Elements

Element: A substance that cannot be separated or broken down into
simpler substances by chemical means.

Each element is defined by unique physical and chemical properties that can
define it.

http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/75006.htm
Atomic Structure

Proton – A subatomic particle that has a positive charge and is located in the
nucleus

The number of protons = atomic number

Neutron – A subatomic particle that has no charge and is located in the
nucleus

Electron – A subatomic particle that has a negative charge and is located in
the nucleus.

Nucleus – A small region in the center of the atom.


Does the nucleus have a positive or negative or neutral charge?
Electron Cloud – The area around the nucleus where the electrons are located.

Why do the electrons not fly off into space? Why do they continue to travel around
the nucleus?
Label the Protons, Neutrons, and
Electrons, nucleus, and electron
cloud.
Atomic Number & Atomic Mass

Atomic Number: the number of protons in the nucleus of the atom.


Does the atomic number equal the number of electrons in an uncharged
atom?
Atomic Mass: The sum of the number of protons and neutrons in an atom.
The mass of an electron is so small, that it is not included in the mass of the
atom.

The mass of 1 proton = the mass of 1,840 electrons
Isotopes & Average Atomic Mass

Isotope: One of two or more atoms that have the same number of protons
(atomic numbers), but different numbers of neutrons (atomic mass)


Remember atoms are characterized by their atomic numbers. Having a
different number of neutrons or atomic mass would not change the atom into a
different element. It just changes the atomic mass.
Average Atomic Mass: The average of mass of all known isotopes of an
element.
Assign the following labels
Labels

Average Atomic Mass

Atomic Number

# of Protons

# of Protons and neutrons
Fill in the concept map
Word List:
Neutrons
Atomic Number
Electrons
Atoms
Atomic Mass
Isotope
Valence Electrons and Periodic
Properties

Elements are arranged in columns, which are called groups.

Valence Electrons – the outermost electrons in an electron cloud. The chemical
properties of an element are largely determined by the valence electrons.

Within each group (or column) the atoms generally have the same number of
valence electrons.

Groups 1 – 2 : atoms have the same number of valence electrons as the group number

Groups 3 -12: 2 or more valence electrons

Groups 13 – 18: valence electrons = group # - 10

Group18: 8 valence electrons = Stable, unreactive.

All atoms “want” to have 8 valence electrons. Atoms are seeking stability.

Elements with only 1-3 valence electrons (mostly metals) , lose electrons easily. 4 – 5
valence electrons (Non-metals) gain electrons easily.
Valence Electrons and Periodic
Properties

Groups 1 – 2 : atoms have the same number of
valence electrons as the group number

Groups 3 -12: 2 or more valence electrons

Groups 13 – 18: valence electrons = group # - 10

Group18: 8 valence electrons = Stable, unreactive.

Elements with only 1-3 valence electrons (mostly
metals) , lose electrons easily. 4 – 5 valence electrons
(Non-metals) gain electrons easily.
Ch.4 S .2 Combinations of Atoms

Compound – A substance that is made up of two or more atoms of
elements joined by chemical bonds


Ex: H2O, CO, CO2, CoI3
Molecule – The smallest unit of a compound that can exist by itself and
retain all of the compound’s chemical properties.

Example: Oxygen – always found as at least O2 , never any less
Chemical Formulas

Chemical formula – a combination of letters and numbers that shows
which elements make up a compound. Also, shows the numbers of atoms
of each element required to make up a molecule of a compound.

H2O

How many atoms of hydrogen are in a molecule of water? How many
atoms of a oxygen are in a molecule of water?
Chemical Equations

Reactions of the elements and compounds are described using a
chemical equation

EX: CH4+2O2→CO2+2H2O

“One molecule of methane reacts with 2 molecules of Oxygen to make one
molecule of carbon dioxide and 2 molecules of hydrogen”
Balancing Chemical Equations

You cannot change the chemical formulas or the subscripts – ONLY THE
COEFFICIENTS

Balance the formula by adding to the coefficients.


EX: H2+ O2 + H2O
Try this one:
Magnesium gas, Mg, reacts with Oxygen gas, O2 to form MgO. Write a balanced
equation for the reaction.
Chemical Bonds

Chemical Bonds: The forces that hold chemicals together


Electrons involved in bonding are only the valence electrons
Ion: A particle or atom that carries a charge

Example: A neutral sodium atom has a charge of zero (equal # of protons and neutrons) and only 1 valence
electron. Once it loses that valence electron, it will have 8 valence electrons and be stable and most likely,
not gain or lose anymore electrons. What would be the charge on a sodium atom that loses one electron?
Chemical Bonds

Ionic Bond: The attractive force between oppositely charged atoms, which form when electrons are
transferred between atoms or molecules

EX: NaCl

How many valence electrons does a neutral sodium atom have?

How many valence electrons does a neutral chloride atom have?

What do you think will happen when the two come into contact with one another?
Chemical Bonds

Covalent bond: A bond that is formed when atoms share one or more pairs of electrons.

EX: Cl2

How many valence electrons does a neutral chloride atom have?

If two chloride atoms came together, could they give or donate electrons as that they both have 8 valence
electrons?
Chemical Bonds

Polar Covalent Bonds: Covalent bonds that do not share electrons equally

Ex: H2O

The oxygen attracts the electrons more strongly than the hydrogen, so the electrons tend to be more
crowded near the oxygen end.

In a molecule of H2O, which area is more negative (The hydrogens or the oxygen)? Which area is more
positive? Why?
Chemical Bonds

Mixtures
Mixture: A combination of two or more substances that are not chemically combined.

Heterogeneous: mixtures in which two more substances are not uniformly distributed


You can easily identify the different parts in this mixture
Homogeneous: A homogeneous mixture has the same composition and properties throughout. This is also called a
solution.

You cannot easily identify the parts that make up the mixture.

Write down an example of a heterogeneous mixture and homogeneous mixture

Is Milk a mixture?
Review

What is the difference between an ionic bond and covalent bond?

What is a compound? What is the difference between a compound and a mixture?

Do the chemical properties of the components of a mixture stay the same or change?

Balance the equation: N2+ H2 → NH3