CHEMISTRY Basic Chemistry

BASIC TERMS ATOM Smallest particle of a chemical element. –Consists of 3 parts. Protons = (+) charge Electrons = (-) charge Neutrons = (no charge)

Section 6.1 Summary – pages The Structure of an atom Nucleus Electron energy levels The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e - ) This region of space is referred to as an electron cloud.

Atom Structure Nucleus – center of an atom. * contains protons / neutrons. * 99.9% of an atoms mass. Electrons – found in electon clouds (orbitals) outside the atom. * 1/2000 of an atoms mass.

Opposite charges attract. Strong charges of protons hold electrons in their orbits around the nucleus

Atomic mass unit – The SI unit for masses of particles in an atom. Atomic Number - the # of protons in the nucleus of an atom. Mass Number – Total number of protons and neutrons in an atom. Atomic Mass – the weighted average of the masses of all naturally occurring isotopes of an element.

Section 6.1 Summary – pages Atoms of the same element always have the same number of protons but may contain different numbers of neutrons. Isotopes of an Element Atoms of the same element that have different numbers of neutrons are called isotopes (I suh tophs) of that element.

Chemical Bonds / Compounds 90 different elements in nature. Most link up in different arrangements. * H 2 O *NaCl A substance formed by the bonding of atoms in definite proportions is a Chemical Compound.

Question 1 Which of the following is an element? (TX Obj 4; 7E) D. water C. sodium chloride B. carbon A. chlorophyll

The answer is B. An element can't be broken down into simpler chemical substances. Chemical elements combine in different ways to form a variety of substances useful to living things.

Table 6.1 Some Elements That Make Up the Human Body ElementSymbol Percent By Mass in Human Body Element Symbol Percent By Mass in Human Body Molybdenum Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Sodium Chlorine Magnesium Selenium Iron Zinc Copper Iodine Manganese Boron Chromium Cobalt Fluorine O C H N Ca P K S Na Cl Mg Fe Zn Cu I Mn B Cr Mo Co Se F trace

The smallest particle of an element that has the characteristics of that element is a(n) __________. (TX Obj 4; 7E) Question 2 D. atom C. nucleus B. electron A. proton

The answer is D. Atoms are the basic building blocks of all matter and have the same general structure, including a nucleus and electrons. Elements found in both living and nonliving things are made of atoms. Nucleus Electron energy levels An atom has a nucleus and electrons in energy levels.

Which of the following can contain two types of particles? (TX Obj 4; 7E) D. electrons Question 3 B. protons C. neutrons A. nucleus

The answer is A. The nucleus is the center of the atom and may contain both positively charged particles and particles that have no charge. Nucleus 8 protons (p+) 8 neutrons (n 0 ) Oxygen atom

2 types of bonds Bonds * Ionic Bonds * Covalent Bonds

When 2 atoms approach each other - they become more stable when e’s are transferred from one atom to the other. Both atoms become ions. - an ion is an atom that has gained or lost 1 or more e’s. Opposite charges attract. - (+) charged ion attracts the (-) ion. The strong attraction between oppositely charged particles is an ionic bond. (see pg. 29 fig. 2-3) Ionic Bonds

Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms. How covalent bonds form For many elements, an atom becomes stable when its outermost energy level is full. Sharing electrons with other atoms is one way for elements to become stable.

Section 6.1 Summary – pages Two hydrogen atoms can combine with each other by sharing their electrons. How covalent bonds form Each atom becomes stable by sharing its electron with the other atom. Hydrogen molecule

Electrons are shared between 2 atoms. - allows both atoms to become stable. For an atom to be stable, all orbitals must be full. - 1 st orbital holds 2 e’s (see pg. 28 fig. 2-2) - all others hold 8 e’s Covalent Bonds

The more e’s in a covalent bond, the stronger the 2 atoms are joined together. 2 e’s = single covalent bond 4 e’s = double bond 6 e’s = triple bond (see pg. 29 fig. 2-3)

Molecules Shared e’s help both atoms become stable. * Covalent bonds do not break easily. Group of atoms united by covalent bonds act as a single unit called a ___________. Molecule

A molecule may contain as few as 2 atoms or up to thousands or millions. Table sugar sucrose contains 45 atoms. DNA contains millions of atoms.

Chemical Formulas Shorthand notation for chemical compounds. Examples H 2 O C 6 H 12 O 6 NaCl

Question 4 B. Sodium and chlorine atoms have no overall electrical charge. A. Sodium and chlorine are sharing electrons in their outer energy levels. Sodium and chlorine combine to form table salt. What do you know to be true? (TX Obj 4; 7E )

Question 4 D. Sodium and chlorine atoms in table salt have full outer energy levels. C. Sodium and chlorine are less stable in the compound sodium chloride. Sodium and chlorine combine to form table salt. What do you know to be true?

The answer is D. Sodium and chlorine atoms combine because the resulting compound, table salt, is more stable than the individual atoms. Sodium loses an electron in its outer energy level, chlorine gains that electron in its outer energy level, and an ionic bond is formed.

pH Scale Used to indicate the strength of solutions. * Solutions with a pH of 7 = neutral. Acids have a pH below 7. * Produce H (+) ions. Bases have a pH above 7. * Produce OH (-) ions.