Chemistry
1
I. Atoms
Protons
Neutrons
Electrons
A. Protons – positively charged�The number of protons defines the element
Figure 2.2
B. The Neutrons (no charge)
Isotopes of Carbon
Figure 2.3
Carbon always has 6 protons; the different isotopes (different number of neutrons) all bond the same way
All isotopes interact with other atoms in the same way and can be used as tracers
Radioactive isotopes are used in experiments and in medicine
Scans of the thyroid gland using a radioactive isotope of iodine
C. Electrons (negatively charged)�The number of electrons determines bonding properties (bonds hold atoms together)
In a neutral atoms, protons = electrons
Electrons are important in bonding because they are on the outside, so when atoms bump into each other, the electrons interact
Electrons are found at various energy levels around the nucleus (2 electrons in the first, 8 in the second)
Valence (outer) Shell- stop interacting when full;
Get full by sharing, giving, or stealing electrons from another atom.
The type of bond made depends on how strongly the nucleus holds in the electron(s).
The attraction of a particular atom for shared electrons is called its electronegativity.
The more electronegative an atom is, the more strongly it pulls shared electrons toward itself.
Ion – charged particle (atom or molecule)
Some atoms are so electronegative that they can steal electrons from other atoms
Atoms that lose electrons become positive ions (cations)
Atoms that gain electrons become negative ions (anions)
What moving, charged particle is responsible for the electricity in your computer or in your home?
The electricity of the body is also moving charges, but NOT electrons….
The electricity of mitochondria is also charges, but not electrons……
II. Types of Chemical Bonds �A. Covalent Bonds
formed when atoms share two or more electrons
Electron sharing produces molecules
Covalently bonded molecules do NOT dissociate (separate) in water. (They might dissolve (mix)).
Ex. Peptide bonds are covalent bonds that are found between amino acids in a protein
Ex. Disulfide bonds are also covalent bonds that are found in a proteins (between sulfur atoms in the R groups)
1. Polar and Nonpolar Covalent Bonds
1. Polar and Nonpolar Covalent Bonds
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Polar molecules – lopsided molecule with polar bonds (hydrophilic).
Water is a Polar molecule
Nonpolar molecule – molecule does NOT have a funky charge distribution – electrons are evenly shared or
or evenly distributed around the molecule
II. Types of Chemical Bonds� B. Ionic Bonds
a positively charged ion and a negatively charged ion are attracted to each other; this force of attraction is an ionic bond
Ionic compounds dissolve (mix) and dissociate (separate) in water, producing individual ions
How will water arrange itself around these ions?
Spheres of hydration (or hydration shell) around two charged ions
II. Types of Chemical Bonds �C. Hydrogen Bonds
An attractive interaction between the partially negative part of one polar molecule (O,N,F) and a hydrogen atom (partially positive) in a molecule
Hydrogen bonds may form between two different molecules
Hydrogen bonds may also form between two different parts of the same molecule
Hydrogen bonds are very weak (but lots of them can make a difference)
What part of DNA is held together by strong covalent bonds? Which part of DNA is held together by weak hydrogen bonds?
II. Types of Chemical Bonds �D. Hydrophobic Interactions
Nonpolar molecules are shunned by water (water tends to be attracted to other water molecules, not to totally neutral molecules).
II. Types of Chemical Bonds �E. More stuff, sort of
Van der Waals forces which cause charge fluctuations in neural molecules, blah, blah, blah
Bonds important in proteins
III. Emergent properties of water
Four emergent properties of water
Hydrogen bonds hold water molecules together and help it to stick to itself
Hydrogen bonds help water to stick to other polar molecules, too
Water has a very high specific heat (it takes a lot of heat for water to change temperature)
Much of the heat is used to disrupt the hydrogen bonds before the water molecules can begin moving faster (or if temp drops, many additional hydrogen bonds form)
Water has a high heat of vaporization (it takes a lot of heat to change water from liquid to gas)
Evaporative cooling – as water evaporates, the surface of the water cools (the most energetic molecules leave – the slower ones are left behind)
Also true for trees – yay for transpiration!
4. Versatility as a solvent (a capacity to dissolve or repel substances)
Vocab
Solvent = the that does the dissolving
Solute = the that gets dissolved
liquid
thing
Sol ent
Solute
Come on in, Lu, the water’s great!
Solutions are mixtures in which one substance is dissolved in another (includes the solute and the solvent).
Aqueous Solutions – water is the solvent.
mix
hydrophilic
“hydro” means water
fire hydrant
dehydrated
hydroplaning
“philic” means “ ”
to love
attracted
Hi. I’m Phil, the Polar Bear. I love water.
repelled
hydrophobic
Phobic means “ ,” like arachnophobia
fear of
This is important in cell membranes. The phospholipids have a heat that is hydrophilic (mixes with water!), and tails that don’t mix with water (keeps the inside of the cell separate from the outside)
Water
Water
How does hydrogen bonding help produce each of the emergent properties of water? Draw/explain
Adhesion & Cohesion
Versatile Solvent
Lighter When Frozen
Moderates Temperature
V. Solute Concentrations
Living things are made of water and other stuff, so we need to know how much (mass) of a solute is there to see how the chemical reactions are going to go…
Molecules are too small to weigh, so we weigh them in moles.
A mole is big, 6.02x1023 things
For aqueous solutions, we talk about the number of moles of something in one liter of water. This is called molarity.
Molarity is a concentration
VI. Acids and Bases
In pure water, sometimes a hydrogen ion is transferred from one water molecule to another, resulting in two ions of opposite charge
Dissociation of Water
This happens in pure water so rarely, that the concentration of a hydrogen ion in pure water is 1x10-7 M (or pH 7)
From your formula sheet:
Acids
H+
HCl 🡪 H+ + Cl-
Bases
NaOH 🡪 Na+ + OH-
H+ + OH– → H2O
lower
higher
QUIZ TIME
Which is the strongest acid?
QUIZ TIME
Which is the weakest base?
QUIZ TIME
Which is the strongest base?
QUIZ TIME
Which is the weakest acid?