Download Elements, Compounds, Bonds

Elements, Compounds, Bonds
Matter
How is it organized?
Elements, Atoms & Compounds
• Element: simplest type of matter with unique
chemical properties
– 92 elements occur naturally
• Atom: Smallest particle of an element that has
the chemical characteristics of that element
• Compound: Substance containing two or more
elements in a fixed ratio
Atoms
• Composed of three
subatomic particles:
– protons (+) & neutrons (0)
make up the nucleus
– electrons (-, e-) in orbitals
(clouds)
Periodic Table
Atoms
• Mass of atom = summed mass
of its protons and neutrons
– 1 proton = 1 atomic mass unit
or amu
– 1 neutron ~1 amu
• Mass = Atomic weight
Summary of subatomic particles
Mass (amu)
Charge
Location
Proton
1
+
Nucleus
Neutron
~1
0
Nucleus
Electron
~0
“Orbitting”
nucleus
Approximate atom
electron (-)
nucleus
proton (+)
neutron (0)
Pea = nucleus
Atoms
• Stable atoms always have same # protons. #
protons = atomic #
– Carbon [C] = 6
• Atoms may have differing #’s of neutrons. #
protons + # neutrons = Atomic weight (mass
number)
– 12C has 6 protons and 6 neutrons
– 13C has 6 protons and 7 neutrons
Periodic Table
Importance (by weight)
Valence and reactivity
• Remember: electrons are
arranged in valence shells
or energy levels that
“orbit” the nucleus.
• # of electrons in atoms
influence their reactivity,
relative to other atoms.
2 electrons
2 electrons
8 electrons
Atoms with unfilled electron
shells are reactive…
• Atoms are “greedy” (want full e- orbitals) and
“lazy” (don’t want to work hard to achieve
them)
• Results in formation of chemical bonds
• Three types of bonds
– Ionic bonds
– Covalent bonds
– Hydrogen bonds
Ionic bonds
• Ionic bonds form between anions (atoms that stripped
an e- from another atom) and cations (atoms that lost
an e-)
• Salts form by ionic bonding
• Basically, a strong electrostatic attraction
Covalent bonds
• Covalent bonds form
when atoms share e-.
– Single or double
• H-H (H2)
• O=C=O (CO2)
• # of bonds formed = #
of e- needed to fill
outer shell
Non-polar Covalent bonds
• Equal sharing of e– Nuclei of similar size
have similar
elecronegativity: pull
on shared electrons in a
covalent bond
Polar Covalent bonds
• Form due to unequal
sharing of e• Relative size and
electrical attraction
of nuclei differ
• Partial + and partial
– sides of molecule
result
Hydrogen bonds
• Weak attraction between
opposite charged poles of
polar molecules
• IMPORTANT bond
– determines structure of large,
complex molecules
– Produces cohesion (water
droplets)
Water is a solvent
• It’s polar; slides
between inorganic
compounds bound by
ionic bonds;
dissociation
• Dissolves ions
• Dissolves organic
molecules with charged
parts (hydrophilic;
“water loving”)
Lubricates
• H-bonding causes water
molecules to adhere to
each other
– Creates thin, but
unbroken film
– Perfect for coating and
lubricating moving parts
pH of common stuff
• Acids donate H+ ions
• Bases accept H+ ions
• Pure water and human
blood are neutral
• Humans run a little
acidic
Hydrogen bonds give H20 it’s
amazing properties
Structural bonds
• Responsible for
secondary structure of
proteins
• α-helix
• β-pleated sheet
Allow water transport
• H-bonding creates surface tension between
water molecules
• As H20 evaporates, it pulls “attached” H20
molecules along with it
Ionic & covalent bonds form:
• Molecules: atoms held together by covalent
bonds
– H20, O2, H2, CO2
• Compounds: chemical substance made of
atoms of 2 or more elements, regardless of
type of bond joining them.
– H20, NaCl, CO2.
Concept Check
•
The reactive properties or chemical behavior of an atom
mostly depend on the number of
1)
2)
3)
4)
the electrons in each electron shell of the atom.
the neutrons found in the nucleus.
the filled electron shells.
the electrons in the outer electron shell of the atom.
Answer
•
The reactive properties or chemical behavior of an atom
mostly depend on the number of
4)
the electrons in the outer electron shell of the atom.
Concept Check
•
Water molecules form
hydrogen bonds because
1)
2)
3)
4)
the water molecule is polar.
the oxygen molecule is
positively charged.
the water molecule forms a
tetrahedron.
the hydrogen atoms are
negatively charged.
Answer
•
Water molecules form
hydrogen bonds because
4) the water molecule is
polar.