Chapter 2 Chemical Basis of Life

I. Elements & Matter A. Matter - Matter refers to anything that has mass and takes up space. - Atoms are the smallest particles of matter.

Elements and Atoms B. Elements 1. All matter is composed of elements 2. Elements are the basic substances that make up matter 3. Atoms are the smallest particles of matter 4. Living Organisms require about twenty elements –95% of human body is made of oxygen, carbon, hydrogen, and nitrogen

Carbon, hydrogen, oxygen, and nitrogen Make up the bulk of living matter Table 2.1

5. Trace elements are common additives to food and water –Dietary deficiencies in trace elements can cause various physiological conditions Figure 2.2A Figure 2.2B

C. Atomic Structure 1. Protons (+) 2. Neutrons (neutral) 3. Electrons (-)

4. Electron arrangement determines the chemical properties of an atom 5. Are arranged in shells, which may contain different numbers of electrons 1 st - 2 electrons2 nd - 8 electrons 3 rd - 18 electrons4 th - 32 electrons Hydrogen (H) Atomic number = 1 Electron Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Outermost electron shell (can hold 8 electrons) First electron shell (can hold 2 electrons )

Drawing Bohr Models of Atoms

D. Periodic Table of Elements

Periodic Table of Elements

How many protons, neutrons, and electrons? Step 1: Use your periodic table to find and element. Step 2: The number of protons (+ charge) The atomic number= 36 Kr has 36 protons

Step 3: The number of electrons (- charge) Remember atoms have no overall charge Atoms must have an equal number of protons and electrons Number of protons = number of electrons Kr has 36 electrons

Step 4: The number of neutrons (neutral/no charge) Mass number (atomic weight rounded to the nearest whole number) Neutrons= mass number – protons Kr neutrons = 84 – 36 = 48

Summary: Number of protons = atomic number Number of electrons = protons Number of neutrons = mass number – protons

Problems: 1. Find the protons (p+), electrons (e-), and neutrons (n) of Oxygen.

Problems: 2. Find the p+, e-, n of Xenon (Xe).

Problems: 3. Find the p+, e-, and n of Zirconium (Zr).

E. Atom Rules # of Protons = Atomic number # of Protons = # of Electrons Mass # = Protons + Neutrons SymbolAtomic#Mass #pne-e- U92192 Na1123 Mg24 Cu65

F. Isotopes 1. Isotopes have a different number of neutrons but the same number of protons 2. Radio active isotopes are used to detect problems with the thyroid, treat cancer, and detect problem with digestion

Isotopes Table 2.4

G. Molecules and Compounds 1. Molecule: when two or more atoms combine (usually for nonmetals) 2. Compound: when two or more atoms of different elements combine –Two types Ionic Covalent

3. Elements can combine to form compounds Sodium Chlorine Sodium Chloride

II. Bonding A. Atoms whose shells are not full, tend to interact with other atoms and gain, lose, or share electrons. These interactions form chemical bonds

B. Types of Bonding 1. Ionic –A metal and non metal –Form ions Na + O 2- –Transfer of electrons –Ionic compounds –Ions are important muscle contraction, nerve impulse transmission, etc.

Ionic bonds are attractions between ions of opposite charge Transfer of electron Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) Na Cl Na + – – – Figure 2.7A

2. Covalent –2 or more non metals –Sharing of electrons forms a bond. Single double or triple –Molecules formed when two or more atoms combine

C. Unequal electron sharing creates polar molecules –A molecule is nonpolar When its covalently bonded atoms share electrons equally

–In a polar covalent bond Electrons are shared unequally between atoms, creating a polar molecule (–) (+) O H H

C. Hydrogen Bond –Occurs when an atom of hydrogen has a strong attraction to two atoms instead of one –The atoms must be highly electronegative (electron loving) like Oxygen, Flourine, Nitrogen, Chlorine and Bromine