Slide 1 of 40 Copyright Pearson Prentice Hall 2-1 The Nature of Matter (Basic Chemistry Review)

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Copyright Pearson Prentice Hall

2-1 The Nature of Matter (Basic Chemistry Review)

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TN State Standards

• Learning Targets

I can:

-describe the parts of an atom

-describe uses of isotopes

-compare and contrast ionic vs. covalent bonding

CLE 3216.3.4


2-1 The Nature of Matter

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Matter

•Matter is anything that has mass and takes up space

•Matter exists in three(four) states:

–Solid

–Liquid

–Gas

–Plasma (very rare)



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Atoms

Atoms

The study of chemistry begins with the basic unit of matter, the atom.

The Greek philosopher Democritus called the smallest fragment of matter the atom, from the Greek word atomos.

Placed side by side, 100 million atoms would make a row only about 1 centimeter long.

Atoms contain subatomic particles that are even smaller.


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Atoms

The subatomic particles that make up atoms are

• protons

• neutrons

• electrons


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Atoms

The subatomic particles in a helium atom.


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Atoms

Protons and neutrons have about the same mass.

Protons are positively charged particles (+).

Neutrons carry no charge(=).

Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom.


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Atoms

The electron is a negatively charged particle (−) with 1/1840 the mass of a proton.

Electrons are in constant motion in the space surrounding the nucleus or electron cloud.

Electrons are attracted to the positively charged nucleus but remain outside the nucleus because of the energy of their motion.

Because atoms have equal numbers of electrons and protons, and because these subatomic particles have equal but opposite charges, atoms are neutral


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Elements and Isotopes


A chemical element is a pure substance that consists entirely of one type of atom.

Elements are represented by a one- or two-letter symbol.

• C stands for carbon.

• Na stands for sodium.


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The number of protons in an atom of an element is the element's atomic number.

Carbon has 6 protons, so its atomic number is 6.

More than 100 elements are known, but only about two dozen are commonly found in living organisms.


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Elements

•All matter is composed of 92 naturally occurring elements.

•Elements cannot be broken down into simpler substances with different chemical or physical properties.

•6 elements (carbon, hydrogen, oxygen, phosphorus, nitrogen and sulfur) make up 95% of the bodyweight of living organisms.



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Isotopes

Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.

The sum of the protons and neutrons in the nucleus of an atom is called its mass number.

Isotopes are identified by their mass numbers.

For example, carbon has three isotopes—carbon-12, carbon-13, and carbon-14. Each isotope has a different number of neutrons


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Isotopes of Carbon

6 electrons6 protons6 neutrons




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Radioactive Isotopes

Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time.

Although the radiation these isotopes give off can be dangerous, they have important scientific and practical uses.


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Radioactive isotopes can be used:

• to determine the ages of rocks and fossils.

• to treat cancer.

• to kill bacteria that cause food to spoil.

• as labels or “tracers” to follow the movement of substances within an organism.


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Chemical Compounds

Chemical Compounds

In nature, most elements are found combined with other elements in compounds.

A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.

The physical and chemical properties of a compound are different from the elements from which it is formed.


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Chemical Compounds

Scientists show the composition of compounds by a kind of shorthand known as a chemical formula.

Water, H2O, contains two atoms of hydrogen for each

atom of oxygen.

The formula for table salt, NaCl, indicates that sodium and chlorine combine in a 1 : 1 ratio.


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Target Check

• 1. List the parts of an atom and their charge.

• 2. Isotopes are atoms of the same element with different numbers of _______.

• 3. How would a radioactive isotope, like Carbon-14, be used to date archeological artifacts?

• 4.What and how many atoms are in the compound H2O?

• 1. Proton (+), Neutron (=), & Electron (-)

• 2. Neutrons

• 3.Carbon-14 turns to Carbon-12 over time. Archeologist measure the amount of C-14 to date the artifact.

• 4. Two Hydrogen atoms and One Oxygen



Slide 19 of 40

Boardwork

• 1. What are the parts of an atom?

• 2. What is the smallest unit of matter?

• 3.What is an isotope?

• 1. proton(+), neutron (=), electron (-)

• 2. The atom

• 3. An atom of an elements with a different number of neutrons.



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Chemical Bonds

Chemical Bonds

The atoms in compounds are held together by chemical bonds.

Bond formation involves the electrons that surround each atomic nucleus.

The electrons that are available to form bonds are called valence electrons.


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Chemical Bonds

The main types of chemical bonds are:

• ionic bonds

• covalent bonds


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Chemical Bonds

Ionic Bonds

An ionic bond is formed when one or more electrons are transferred from one atom to another.

An atom that loses electrons has a positive charge.

An atom that gains electrons has a negative charge.

These positively and negatively charged atoms are known as ions.


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Chemical Bonds

Protons +17Electrons - 18

Charge -1


Charge 0


Charge +1


Charge 0

Chloride ion (Cl-)

Sodium atom (Na) Chlorine atom (Cl)

Sodium ion (Na+)


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Chemical Bonds

Covalent Bonds

Sometimes electrons are shared by atoms instead of being transferred.

Sharing electrons means that the moving electrons actually travel in the orbitals of both atoms.


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Chemical Bonds

A covalent bond forms when electrons are shared between atoms.

• When the atoms share two electrons, the bond is called a single covalent bond.

• When atoms share four electrons it is called a double bond.

• When atoms share six electrons it is called a triple bond.


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Chemical Bonds

The structure that results when atoms are joined together by covalent bonds is called a molecule.

A molecule is the smallest unit of most compounds.


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Chemical Bonds

In a water molecule, each hydrogen atom forms a single covalent bond with the oxygen atom.


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Chemical Bonds

Van der Waals Forces

When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules.

Chemists call such intermolecular forces of attraction van der Waals forces, after the scientist who discovered them.

Although van der Waals forces are not as strong as ionic bonds or covalent bonds, they can hold molecules together, especially when the molecules are large.


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Chemical Bonds

For example, Van der Waals forces(+/-) form between the molecules on the surface of a gecko’s foot and the molecules on the surface of the wall.

The combined strength of all the van der Waals forces allows the gecko to grip the wall.

- or -Continue to: Click to Launch:

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2-1

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2-1

The particles that move around the nucleus of an atom are called

a. neutrons.

b. protons.

c. electrons.

d. isotopes.

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2-1

The atomic number of a carbon atom is 6. How many neutrons does the isotope carbon-14 have?

a. 6

b. 8

c. 12

d. 14

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2-1

Which of the following statements about the three isotopes of carbon is true?

a. They are all radioactive.

b. They have different numbers of electrons.

c. They have the same chemical properties but differ in atomic mass.

d. They have the same number of protons and neutrons.

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2-1

A chemical compound consists of

a. electrons mixed with neutrons.

b. two or more elements combined in a definite proportion.

c. two or more elements combined in any proportion.

d. at least three elements combined by ionic or covalent bonds.

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2-1

Van der Waals forces are the result of

a. unequal sharing of electrons.

b. ionic bonds.

c. the bonding of different isotopes.

d. the chemical combination of sodium and chlorine.

END OF SECTION

Slide 1 of 40 Copyright Pearson Prentice Hall 2-1 The Nature of Matter (Basic Chemistry Review)

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