chapter 3 - chemistry
DESCRIPTION
Chapter 3 - Chemistry. A Brief … Overview. Matter. Matter occupies space and has weight. It can exist as a solid, liquid, or gas. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 3 - Chemistry
A Brief … Overview
Matter
Matter occupies space and has weight. It can exist as a solid, liquid, or gas. It may be possible to break some kinds of
matter down into other kinds of matter with different properties. For example, water (H2O) can be broken down into hydrogen and oxygen.
Hydrogen and oxygen in the above example cannot be broken down any further because they are elements.
Elements
Elements cannot be broken down into substances with different properties. For example, water (H2O) is not an element because it can be broken down into hydrogen (H) and oxygen (O).
The smallest particle of an element is an atom. Elements are substances made up of only one kind of
atom. There are 92 naturally occurring elements. Matter is
therefore composed of 92 different kinds of elements. The following elements make up 98% of the body weight
of organisms: Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur, Phosphorus.
Atoms
Characteristics of Subatomic Particles
The mass of subatomic particles is too small to be conveniently measured in grams so atomic mass units (amu) are used instead. Atomic mass units are also called daltons. One amu (or dalton) is approximately 1.7 X 10-24g.
Protons and neutrons have a mass of approximately 1 amu. The mass of an electron is much less. The total mass of an atom is due mostly to the mass of protons and neutrons.
Atomic Weight
The atomic weight is calculated as the sum of the mass of protons, electrons, and neutrons.
The mass of electrons is small enough that we can generally disregard it in our calculations.
Most of an atom is empty space.
Atomic Number
The atomic number is the number of protons.
All atoms of an element have the same atomic number.
The number of protons contributes to the physical properties of an element.
Atoms are neutral, therefore the number of electrons is equal to the number of protons.
Atomic Symbols
Isotopes
Isotopes are atoms that have the same number of protons and differ only in the number of neutrons. Three different forms of hydrogen are shown below
Most isotopes are stable but radioactive isotopes are unstable and break down into more stable forms by emitting radiation.
Radiation can be detected, so radioactive isotopes are useful as labels in scientific research and medical diagnostic procedures.
Energy
Energy is the ability to do work. For example, it takes energy to move matter.
Potential energy is stored energy. Electrons at greater distances from the
nucleus contain more stored energy. Example - Many of the chemical reactions
that are associated with energy (ex: photosynthesis) involve electrons moving to higher or lower energy levels.
Distribution of Electrons
Electron Shells Orbitals The Outer Shell Chemical bonds form when atoms react
to fill their outer shells with electrons. A compound is two or more elements
joined together by chemical bonds.
Periodic Table of the Elements
http://www.dreamwv.com/primer/page/s_pertab.html
Ionic Bonding• Ionic bonding is the transfer of electrons from one atom to another.
• Atoms that have lost or gained electrons are called ions. The gain or loss of electrons results in ions having a positive or negative charge.
Activity
Draw a calcium atom. Draw a chlorine atom. Use circles to represent electrons and tell how many protons and neutrons are in the nucleus. Draw calcium chloride.
Covalent Bonds
Covalent bonds form when atoms share electrons.
Hydrogen atoms contain one electron and one proton.
In the diagram, two hydrogen atoms are bonded by a single covalent bond. The two atoms each share a pair of electrons.
Molecules
CH4
Double and Triple Bonds
A Shorthand Method for Drawing Covalent Bonds
Polar Covalent Bonds
When the atoms share the electrons equally, the molecule is nonpolar.
Polar molecules are formed when two different size atoms are covalently bonded. The molecule is polar because the electrons are not shared equally between the two atoms; the electrons spend more time with the larger atom.
Cont’d
Hydrogen Bonds
Activity
Draw two atoms that are bonded by a single covalent bond. Draw 2 atoms bonded by a double covalent bond and 2 bonded by a triple covalent bond. Finally, draw two atoms that are bonded by a polar covalent bond. Use any hypothetical atoms. After your diagrams are complete, identify the atom. Use the periodic table if necessary.
Chemical Equations
Not Balanced
Balanced
Important Concepts Regarding Covalent Bonds
Energy and Covalent Bonds Energy is required to form a covalent
bond and energy is released when a Covalent bond is broken. Covalent bonds can therefore be used to store energy.
Oxidation-Reduction Reactions Oxidation is the loss of
elecrons or the loss of hydrogen atoms from an atom or molecule. As a result, energy is released.
Reduction is the gain of electrons or the gain of hydrogen atoms. This process stores energy.
Oxidation and reduction occur together. When a atom or molecule is oxidized, another must be reduced.
Redox Reaction
Water
Life evolved in water. Living things are 70-90% water. In nature, water is a solvent for many kinds of chemical reactions.
Water is a polar molecule because the hydrogen atoms are much smaller than the oxygen atoms and also because the molecule is arranged so that the two hydrogen atoms are on one side while the oxygen is on the other.
Cont’d Ions Separate
(Dissolve) in Water
Cont’d Water molecules
adhere to polar molecules.
Cont’d The temperature of water changes
more slowly than that of other liquids.
It takes 1 calorie of heat to raise the temperature of 1 gram of water 1° C. To raise the temperature of an equal volume of air 1° C takes 0.0003 calories. Water requires 3000 times
more energy than air.This property protects organisms from rapid temperature
changes.
Cont’d Water resists changing to a solid or a
gas.
Ice is less dense than water.
Ionization of Water
Acids and Bases
HCl H+ + Cl-
NaOH Na+ + OH-
H2O H+ + OH-
pH
The measure of the strength of an acid or base is called the pH. It is a measure of the concentration of hydrogen ions (H+).
The pH ranges from 0 to 14. An acid has a pH less than 7. A base has a pH greater than 7. A pH of 7 is neutral.