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Biology
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2-1 The Nature of Matter
Photo Credit: © John Conrad/CORBIS
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Atoms
Atoms
The study of chemistry begins with the basic unit of matter, the atom.
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Atoms
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.
Helium atoms contain protons, neutrons, and electrons. The positively charged protons and uncharged neutrons are bound together in the dense nucleus, while the negatively charged electrons move in the space around the nucleus.
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Elements and Isotopes
Elements and Isotopes
A chemical element is a pure substance that consists entirely of one type of atom.
C stands for carbon.
Na stands for sodium.
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Elements and Isotopes
The number of protons in an atom of an element is the element's atomic number.
Commonly found in living organisms:
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Elements and Isotopes
Isotopes
Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.
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Elements and Isotopes
Because they have the same number of electrons, all isotopes of an element have the same chemical properties.
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Elements and Isotopes
Isotopes of Carbon
Because they have the same number of electrons, these isotopes of carbon have the same chemical properties. The difference among the isotopes is the number of neutrons in their nuclei.
6 electrons
6 protons
8 neutrons
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Elements and Isotopes
Radioactive Isotopes
Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time
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Elements and Isotopes
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
A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.
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Chemical Compounds
Chemical Formula
Water
Table Salt
Hydrochloric Acid
Glucose
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Chemical Bonds
Chemical Bonds
The atoms in compounds are held together by chemical bonds.
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.
These positively and negatively charged atoms are known as ions.
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Chemical Bonds
Sodium atom (Na)
Sodium ion (Cl-)
Sodium ion (Na+)
Sodium atom (Cl)
The chemical bond in which electrons are transferred from one atom to another is called an ionic bond. The compound sodium chloride forms when sodium loses its valence electron to chlorine.
Protons
Electrons
Charge
Protons
Electrons
Charge
Protons
Electrons
Charge
Protons
Electrons
Charge
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Chemical Bonds
Covalent Bonds
Sometimes electrons are shared by atoms instead of being transferred.
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Chemical Bonds
A covalent bond forms when electrons are shared between atoms.
single covalent bond
double bond
triple bond
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Chemical Bonds
The structure that results when atoms are joined together by covalent bonds is called a molecule.
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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.
van der Waals forces
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2-1
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2-1
The particles that move around the nucleus of an atom are called
neutrons.
protons.
electrons.
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? 6 8 12 14
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2-1
Which of the following statements about the three isotopes of carbon is true?
They are all radioactive.
They have different numbers of electrons.
They have the same chemical properties but differ in atomic mass.
They have the same number of protons and neutrons.
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2-1
A chemical compound consists of
Electrons mixed with neutrons.
two or more elements combined in a definite proportion.
two or more protons combined in any proportion.
at least three elements combined by ionic or covalent bonds.
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2-1
Van der Waals forces are the result of
unequal sharing of electrons.
ionic bonds.
the bonding of different isotopes.
the chemical combination of sodium and chlorine.
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