The Chemistry of Life Chapter 2 Prof. J. Dodd
Why should we study chemistry in
C, H, O, N
Atoms are composed of 3 main particles: (subatomic particles) Protons (+) Neutrons Electrons (-)
Protons and Neutrons Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom. Both particles have about the same mass.
Atoms have equal numbers of electrons and protons. Because these subatomic particles have equal but opposite charges, atoms are neutral.
Elements Elements are the building blocks of all matter. Elements cannot be decomposed into simpler matter. Group Number: 1 2 3 4 5 6 7 8
Checking Out the Periodic Table of Elements APK: What is an element? Name one!
What is a compound? The goals for today s lesson are: 1. To determine the elements that make up some common compounds. 2. To define the term compound. 3. To discover that all compounds consist of two or more elements. 4. To determine the number of atoms and the elements in some common chemical compounds. 5. To visualize the Periodic Table and understand that it is organized by atomic properties Homework: Chemistry Practice Compounds Sheet
The Elements 110 known elements 88 occur naturally The 110 elements form a plethora of compounds, just as 26 letters of the alphabet make a seemingly endless number of words.
Atomic Number Counts the number of protons in an atom
Atomic Number on the Periodic Table Atomic Number Symbol 11 Na
All atoms of an element have the same number of protons 11 protons Sodium 11 Na
Atomic Mass Mass of an atom. Approximately equal to the number of protons and neutrons Find number of neutrons by subtracting the number of protons from the mass.
Review: An element's atomic number tells how many protons are in its atoms. An element's mass number tells how many protons and neutrons are in its atoms.
Learning Check 1 State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons
Isotopes Isotopes are atoms that have the same atomic number but different mass number. Most elements have two or more isotopes. Same chemical properties because the Proton number does not change.
Isotopes of Carbon Carbon 14 Half-life of 5,730±40 years What does this mean?
More about isotopes: Some isotopes have unstable nuclei which break down over time. They are called radioactive isotopes Some radiation is harmful.
Radiation can also be useful Radioactive Dating Cancer Treatment Kill bacteria Tracers with X-rays
More About Atomic Structure The center of the atom is called the nucleus. Electrons live in something called shells. Shells are areas that surround the center of an atom. A shell is sometimes called an orbital or energy level.
More About Electrons Every shell can hold only so many electrons The further from the nucleus, the more electrons a shell can hold
Valence Electrons The electrons on the outside edge of the atom This is where the action is- where bonding takes place Atoms have no more than 8 valence electrons
The Octet Rule: Atoms will combine to form compounds in order to reach eight electrons in their outer energy level. This is very stable! Atoms with less than 4 electrons tend to lose electrons. Atoms with more than 4 electrons tend to gain electrons.
They interact by sharing an electron, which is called bonding. Here are two hydrogen atoms that are sharing an electron. Both now have a complete first shell of two electrons. This is a sharing (covalent) bond. H 2 represents a molecule of hydrogen. Hydrogen is the first, smallest, and lightest element. It s #1 on the periodic table.
What is a molecule? A molecule is the chemical combination of two or more atoms. Molecules can be of the same element, such as in the oxygen molecule (O 2 ) or two or more different elements as in the water molecule (H 2 O). A molecule is the smallest amount of a compound you can have. Molecules of hydrogen H 2 form because atoms can share electrons. That s why you always see a molecule of hydrogen written H 2..
What is a compound? Substances that are composed of two or more elements are called compounds. For example, water is a compound because it is composed of hydrogen and oxygen. Here is the diagram of a molecule of water Notice the two hydrogen and one oxygen atoms. They are attached by their shared electrons. The chemical formula is H 2 O.
Compound Two or more elements chemically combined in specific proportions Examples: Water H 2 O Salt NaCl Sugar C 6 H 12 O 6 Chemical Formulas are used to represent compounds
Chemical abbreviations are used as a kind of shorthand for writing the names of compounds. Also known as a chemical formula, these abbreviations expresses the exact composition of a molecule or substance using the symbols of the chemical elements. Here are a few common chemical compounds and their abbreviations. What do the formulas mean? carbon dioxide CO 2 carbon monoxide CO methane CH 4 sugar (Glucose) C 6 H 12 O 6
2 types of Compounds? What are they? Ionic Covalent
Ionic Compounds Form when electrons are transferred from one atom to another. Ions - Atoms with a net charge due to gaining or losing electrons Gaining electrons gives an ion a negative charge Losing electrons gives an ion a positive charge **If they have to choose, atoms would rather be stable (with a full octet ) than neutral.
How Does This Happen? Some atoms have a few too many electrons Some atoms only need a few electrons
What do you do if you are a sodium (Na) atom with one extra electron? Go look for an atom that wants it!
Ionic Bonding Negative ions and positive ions are held together by ionic bond.
Ionic compounds form between metals and nonmetals
What If No One Will Give Up An Electron? Atoms with less than 8 valence electrons can move close to each other and share their electrons The electrons spend their time around both atoms. And they lived happily ever after!
Covalent Bonds Formed when a pair of electrons is shared between two atoms. Sometimes the atoms share two pairs of electrons and form a double bond, or three pairs of electrons to form a triple bond. Structures formed by covalent bonds are molecules.
Covalent compounds form between 2 nonmetals
Van der Waals Forces There are small attractive forces between all atoms Help to hold molecules to each other Ex: Gecko
Let s summarize what we know! Why do compounds form? Atoms are trying to get 8 valence electrons How do compounds form? By ionic (e- transfer) or covalent (e- sharing) bonding How can you tell if a compound is ionic or covalent? By the types of elements in the compound (ionic = M + NM covalent = NM + NM)
Learning Check 2: Indicate whether a bond between the following would be 1) Ionic 2) covalent A. sodium and oxygen B. nitrogen and oxygen C. phosphorus and chlorine D. calcium and sulfur E. chlorine and bromine