all matter consists of elements chemistry is the study of matter matter is – anything that has...
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All Matter Consists of Elements• Chemistry is the study of matter• Matter is
– Anything that has mass and occupies space– Composed of elements
• Elements– Cannot be broken down to a simpler form– Periodic table of elements – lists all known
elements
Figure 2.2
Groupnumber
Atomicnumber
Element symbol
Atomic mass
Nonmetals
Metals
Transition elements
Lanthanides
Actinides
Metals Nonmetals
Atoms – Smallest Functional Unit of Elements
• Atoms consist of– Nucleus (central core)
• Protons– positive charge– have mass
• Neutrons– no charge– have mass
– Shells (surrounding nucleus)• Electrons
– negative charge– no discernable mass
Figure 2.3
Electron
Proton
Shell
Neutron
Nucleus
a) Hydrogen 1 proton
b) Oxygen 8 protons 8 neutrons 8 electrons in 2 shells
c) Sodium 11 protons 11 neutrons 11 electrons in 3 shells
More About Atoms• Atomic symbol: one or two letters
– Na: sodium– O: oxygen
• Atomic number– Number of protons
• Atomic mass– Roughly equal to number of protons plus neutrons
• In an electrically neutral atom– Number of protons = number of electrons
Isotopes Have a Different Number of Neutrons
• Same atomic number (same number of protons)
• Different atomic mass (different number of neutrons)
• Unstable isotopes are called radioisotopes• Radioisotopes give off
– Energy (in the form of radiation)– Particles
• Unstable isotopes are called radioisotopes– Give off energy in the form of radiation
• Some radioisotopes have scientific and medical uses– Carbon-14: used for dating fossils– Diagnostic imaging– Cancer treatment– Power supply for implants such as cardiac
pacemakers
Isotopes Have a Different Number of Neutrons
Energy Fuels Life’s Activities
• Energy: the capacity to do work• Potential energy: stored energy• Kinetic energy: energy in motion,
doing work• Potential energy can be transformed into
kinetic energy
Energy Fuels Life’s Activities
• Electrons have potential energy– Each shell corresponds to a specific level of
potential energy– Shells that are farther from the nucleus contain
electrons with more potential energy
• Atoms are most stable when their outermost shell is full
• Atoms will interact with other atoms to fill their outermost shells
Chemical Bonds Link Atoms to Form Molecules
• Chemical bonds: attractive forces holding atoms together
• Kinds of chemical bonds– Covalent bonds– Ionic bonds– Hydrogen bonds
Covalent Bonds• Covalent bonds form when atoms share
electrons • Very strong bonds• Examples
– Hydrogen molecule: H2
– Oxygen molecule: O2
– Water: H2O
Figure 2.5
Writtenformula Structural representation
Structuralformulawithcovalentbond
Hydrogen(H2)
Oxygen
(O2)
Water(H2O)
Two singlecovalent bonds
Single covalent bond
Double covalent bond
Covalent Bonds• Nonpolar covalent bonds: electrons are
shared equally– H2
– O2
– CH4
• Polar covalent bonds: electrons are NOT shared equally– H2O: The oxygen has a stronger pull on the
shared electrons than the hydrogen does
Ionic Bonds• Ion: an electrically charged atom or
molecule• Positively charged ion: forms if an atom or
molecule loses electrons• Negatively charged ion: forms if an atom or
molecule gains electrons• Ionic bond: attractive force between
oppositely charged ions• Example: NaCl
Figure 2.6
Loss of electron:positive charge
Gain of electron:negative charge
Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+)
Sodium chloride molecule (NaCl)
Chloride ion (Cl–)
Hydrogen Bonds• Form between polar molecules• Polar molecules
– Contain polar covalent bonds in which there is unequal sharing of electrons
– Electrically neutral overall, but uneven charge distribution
• Hydrogen bond – Weak attraction between oppositely charged
regions of polar molecules – Example: weak forces between water
molecules
Figure 2.7
Molecule
Oxygen (O)
Hydrogen (H)
Water Ice
Life Depends on Water
• Water molecules are polar
• Water is liquid at body temperature• Water is the biological solvent
• Water can absorb and hold heat energy• Water helps regulate body temperature
Water Is the Biological Solvent• Solvent: liquid in which other substances
dissolve• Solute: any dissolved substance• Hydrophilic: polar molecules that are
attracted to water and interact easily with water
• Hydrophobic: nonpolar neutral molecules that do not interact with or dissolve in water
Figure 2.8
Ionsin solution
Moleculesof water
Salt crystal
The Importance of Hydrogen Ions
• Acids:– Donate hydrogen ions (protons)– Increase hydrogen ion concentration in
solutions
• Bases – Accept hydrogen ions (protons)– Lower hydrogen ion concentration in solutions
• pH Scale– A measure of hydrogen ion concentration
The pH Scale
• Measure of hydrogen ion concentration in solution
• Ranges from 0 to 14– Acids: pH < 7– Neutral: pH = 7– Basic: pH > 7
pH values
Concentrationsof H+
(moles/liter)Drain opener
Bleach
Ammonia cleanser
Soapy water
Baking soda
Human blood, tears
Saliva, urine
Black coffee
Tomatoes
Vinegar, cola
Lemon juice
Hydrochloric acid
Concentrated nitric acid
Mo
re a
cid
ic
Neutral pH
Mo
re a
lkal
ine
14
13
12
11
10
9
8
7
6
5
4
3
2
1
10–13
10–11
10–9
10–7
10–5
10–3
10–1
0Figure 2.10
Buffers
• Minimize pH change• Help maintain stable pH in body fluids• Carbonic acid and bicarbonate act as one of
the body’s most important buffer pairs• HCO3
- + H+ H2CO3
Water and Chemistry
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