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2-1 The Nature of Matter
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2-1 The Nature of Matter
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Atoms
Atoms
Atom – smallest unit of matter
Element - types of atoms.
• C stands for carbon.
• Na stands for sodium.
• 92 naturally occurring elements
• 15 found in living things
• 4 make up 95% of living things (C,H,O,N)
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Chemical Compounds
Molecules – 2 or more atoms
Compounds - two or more elements
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Atoms
The subatomic particles that make up atoms are
Protons
Neutrons
electrons
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Atoms
Protons are positively charged particles (+).
Neutrons carry no charge.
Protons and neutrons have about the same mass.
Nucleus - the center of the atom contains protons and neutrons only.
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Atoms
Electrons - a negatively charged particle (−) with 1/1840 the mass of a proton.
Electrons are located in energy levels around nucleus
1st – 2 max
2nd – 8 max
3rd – 8 max
# protons = # electrons & atoms are neutral.
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Atoms
The subatomic particles in a helium atom.
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Elements and Isotopes
Atomic number - The number of protons in an atom.
Mass number -The sum of the protons and neutrons.
ex) Carbon 12 – 6 protons & 6 neutrons
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Elements of Life
Element Atomic Number
Atomic Mass
Outer electrons
Electrons needed
Bonds formed
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Elements and Isotopes
Isotopes - Atoms of the same element that differ in the number of neutrons they contain.
For example: carbon-12, carbon-13, & carbon-14.
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Elements and Isotopes
Isotopes of Carbon
6 electrons6 protons6 neutrons
6 electrons6 protons7 neutrons
6 electrons6 protons8 neutrons
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Elements and Isotopes
Radioactive Isotopes
The atomic nuclei are unstable and break down at a constant rate over time.
Half-life – time it takes ½ a sample to decay.
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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 formula:
Water, H2O, contains two atoms of hydrogen for each
atom of oxygen.
Table salt, NaCl, indicates that sodium and chlorine combine in a 1 : 1 ratio.
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Chemical Bonds
Chemical Bonds: hold atoms together
Covalent Bonds – sharing of electrons
Single bond – share 1 pair of electrons
Double bond – share 2 pairs of electrons
Triple bond – share 3 pairs of electrons
Polar Covalent Bond – unequal sharing of electrons
Ex.) Water
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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
Ionic Bonds - electrons are transferred from one atom to another.
Ions - positively or negatively charged atoms
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Chemical Bonds
Protons +17Electrons - 18
Charge -1
Protons +11Electrons - 11
Charge 0
Protons +11Electrons - 10
Charge +1
Protons +17Electrons - 17
Charge 0
Sodium ion (Cl-)Sodium atom (Na)
Sodium atom (Cl)Sodium ion (Na+)
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The particles that move around the nucleus of an atom are called
a. neutrons.
b. protons.
c. electrons.
d. isotopes.
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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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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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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.