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2.1 Atoms, Ions, and Molecules
KEY CONCEPT
All living things are based on atoms and their
interactions.
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2.1 Atoms, Ions, and Molecules
Living things consist of atoms of different elements.
• An atom is the smallest basic unit of matter.
• Matter is anything that occupies space and has mass
• An element is one type of atom.
Hydrogen atom (H)
H
Oxygen atom (O)
O
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2.1 Atoms, Ions, and Molecules
• An atom has 2 parts: a nucleus & electrons.
– The nucleus is made up of protons and neutrons.
– Electrons float around in “energy levels” outside nucleus.
Oxygen atom (O)
Nucleus:
8 protons (+)
8 neutrons
outermost energy
level:
6 electrons (-)
inner energy level:
2 electrons (-)
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2.1 Atoms, Ions, and Molecules
• A compound is a molecule containing atoms of different
elements that are chemically combined (bonded) in a
fixed ratio.
– water (H2O)
_
O
H
+
H
+
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2.1 Atoms, Ions, and Molecules
• A compound is made of atoms of different elements
bonded together.
– water (H2O)
– carbon dioxide (CO2)
– There are many other carbon-based compounds in living
things!!
2.1 Atoms, Ions, and Molecules
Warm - Up
• Sketch an atom.
• Label the nucleus, energy levels, electrons, protons, and
neutrons.
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2.1 Atoms, Ions, and Molecules
• The atoms in compounds can bond together in 2
different ways:
– Ionic bonds form when atoms gain or lose electrons to
each other
(Ionic bonds are strong bonds)
– Covalent bonds form when atoms share electrons
(Covalent bonds are weak bonds)
Analogy – baseball teams
Ionic Bonds – 1 player (electron) switches to other team
Covalent – The catcher catches for both teams
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2.1 Atoms, Ions, and Molecules
Ionic bonds form because of “ions”
• An ion is an atom that has gained or lost one or more
electrons.
– positive ions (made when an electron is lost)
– negative ions (made when an electron is gained)
Therefore…Ionic bonds can form form between the
oppositely charged ions!
gained
Na loses an
electron to CI
Sodium atom
(Na)
Chlorine atom
(CI)
electron
ionic bond
Sodium ion
(Na+)
Chloride ion
(CI-)
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2.1 Atoms, Ions, and Molecules
Atoms share pairs of electrons in covalent bonds.
• A covalent bond forms when atoms share a pair of
electrons.
covalent bonds
Oxygen atom (O)
Carbon atom (C)
Carbon dioxide (CO2 )
Oxygen atom (O)
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2.1 Atoms, Ions, and Molecules
Molecules
•
Molecules are formed when 2 or more atoms are held
together by covalent bonds.
•
Chemical formula: tells you the number and types of
atoms in a molecule (example: H2O tells you that
water has 2 hydrogen atoms and 1 oxygen atom)
• Structural formula: shows how atoms in a molecule are
connected (by bonds)
2.1 Atoms, Ions, and Molecules
PRACTICE!!!
1. Determine if each is the chemical or structural formula of
the molecule.
KMnO4
MgSO4
2.1 Atoms, Ions, and Molecules
Chemical Reactions
• Chemical reaction: The breaking apart of old bonds and
forming of new chemical bonds…resulting in a TOTALLY
NEW SUBSTANCE. ( its like a math problem!)
– Reactants: starting materials for a reaction
– Products: ending materials from a reaction
1
+
1
=
2
2.2 Properties of Water
KEY CONCEPT
Water’s unique properties allow life to exist on Earth.
Objectives:
• Describe the structure of a water molecule
• List and describe water’s unique properties
• Distinguish between an acid & base
• Explain how Earth’s conditions are fit for life
2.2 Properties of Water
Life depends on hydrogen bonds in water.
• Water is a polar covalent molecule.
– Polar molecules have slightly charged regions.
– Hydrogen bonds form between slightly positive
hydrogen atoms and slightly negative oxygen atoms.
_
O
H
+
H
+
– Nonpolar molecules do not have charged regions.
2.2 Properties of Water
Hydrogen bonds are responsible for 3 important properties
of water:
1. High specific heat - water must absorb A LOT of heat
before it gets “hot” (increases temp.)
2. Cohesion: tendency of like molecules to stick together
3. Adhesion: type of attraction that occurs between
unlike molecules
2.2 Properties of Water
Cohesion & Adhesion --- DEMO
Cohesion: tendency of
like molecules to stick
together
Adhesion: attraction
that occurs between
unlike molecules
2.2 Properties of Water
Explain this picture using 2 of the 3 unique properties of
water!
2.2 Properties of Water
Many compounds dissolve in water ------ DEMO.
• A solution is formed when one substance dissolves in
another.
– Solvents dissolves other substances. (H2O)
– Solutes dissolve in a solvent. (NaCl)
– Aqueous Solution – any solution where water is the
solvent.
solution
2.2 Properties of Water
“Like dissolves like”
– Polar solvents dissolve polar
solutes.
– Nonpolar solvents dissolve
nonpolar solutes.
– Polar substances and
nonpolar substances generally
remain separate.
2.2 Properties of Water
Some compounds form acids or bases.
• An acid releases a hydrogen ion when it dissolves in
water.
– high H+ concentration
– pH less than 7
stomach acid pH between 1 and 3
more acidic
2.2 Properties of Water
• A base removes hydrogen ions from a solution.
– low H+ concentration
– pH greater than 7
bile pH between 8 and 9
more basic
2.2 Properties of Water
• A neutral solution has a pH of 7.
• See page 85 to view examples of Acids & Bases
pure water pH 7