Chapter 6

 What do you know about atoms?

 The smallest unit of matter  The building blocks of matter

 Atoms are so small that billions of them fit on the head of a pin  Atoms are made up of protons, neutrons, and electrons ◦ Protons and neutrons are located at the center of the atom, called the atomic nucleus  Protons ◦ Positively charged particles  Neutrons ◦ Particles that have no charge  Electrons ◦ Negatively charged particles

 Located outside of the nucleus  Constantly move around the nucleus at different energy levels  The basic structure of an atom is the result of the attraction between protons and electrons

 Let’s create a concept map comparing and contrasting electrons, neutrons, and protons Protons Electrons Neutrons Positively chargedNo charge Negatively charged Make up the atomic nucleus In even amounts of elements Weigh the same Rotate around atomic nucleus or outside Weigh an 1/1800 of a proton Make up an atom

 An element is a pure substance that cannot be broken down into other substances  Made up of only one type of atom  There are over 100 known elements, and 92 of these occur in nature

 Organized into horizontal rows called Periods  Organized into vertical columns called Groups  Each individual block represents an element

 Atoms of the same element that have different numbers of neutrons

 Changing the number of neutrons can affect the stability of the nucleus and in some cases causing the nucleus to decay, or break apart  In some cases, it gives off radiation  The radiation can be detected and used for many applications  Example: Carbon Dating (carbon-14) to calculate the age of an object

 A compound is a pure substance formed when two or more different elements combine  Example: NaCl (Sodium Chloride), H 2 O (Water)

 Always formed with a specific combination of elements in a fixed ratio ◦ Ex: Water is always formed in a ratio of two hydrogen and one oxygen ◦ Each water molecule has the same structure  Chemically and physically different than the elements that comprise them ◦ Ex: Water has different properties than hydrogen or oxygen

 Cannot be broken down into simpler means, such as tearing or crushing ◦ Can be broken down by chemical means into simpler compounds or into their original elements

 Draw the chemical structure of: ◦ H 2 O ◦ CO 2 ◦ NaCl ◦ CO

 The force that holds the substances together  The nucleus determines the chemical identity of an atom  The electrons are involved directly in forming chemical bonds

 Electrons travel around the nucleus of an atom in areas called energy levels  Each energy level has a specific number of electrons that it can hold at any time  The first can hold up to 2 electrons  The second can hold up to 8 electrons

 A partially-filled energy level is not stable  Atoms become more stable by losing electrons or attracting electrons from other atoms  This results in the chemical formation of chemical bonds between atoms  This forming of bonds stores energy (absorb) and the breaking of bonds provides energy (release) for growth, development, adaptation, and reproduction in living things

 Forms when electrons are shared ◦ Ex: H 2 O  Most compounds in living organisms have covalent bonds holding them together  A molecule is a compound in which the atoms are held together by covalent bonds ◦ Ex: H 2 O ◦ Depending on the number of shared electrons, covalent bonds can be single, double, or triple

 Electrical attraction between two oppositely charged atoms or groups of atoms called ions  Ions are atoms that have lost or gained one or more electrons and carries an electric charge ◦ Ex:Na +, Cl -

 Remember: Atoms are neutral  In order for an atom to be most stable, the outermost energy level should either be completely filled or empty.  Some atoms tend to give up (donate) or obtain (accept) electrons to empty or fill the outer energy levels in order to be stable. ◦ This leads to atoms with a charge

 Substances formed by ionic bonds are called ionic compounds  Ions in living things include Sodium, Potassium, Calcium, Chloride, and Carbonate ions  They help to maintain homeostasis as they travel in and out of the cells  They help transmit signals among cells that allow you to see, taste, hear, feel, and smell

 Draw your own covalent and ionic bonds on the whiteboards ◦ Covalent: show electrons shared ◦ Ionic: show electrons that are distributed unequally  Practice with these: NaCl, H 2 O, H 2, O 2, N 2, KCl, NaBr

Covalent Bonds Low PolarityFormed between two non-metalsShare electronsDefinite ShapeExamples: CH4 and HCl Ionic Bonds High Polarity Formed between a metal and non- metal Non-metals are stronger than metal and can get electrons easily No definite shapeExamples: NaCl, H2SO4

 Positive ions and negative ions form based on the ability of an atom to attract electrons  If the nucleus of the atom has a weak attraction for the electron it will donate the electron to an atom with a stronger attraction  Elements in covalent bonds do not always attract electrons equally

 Electrons in a molecule are in random motion around the nuclei. This causes an unequal distribution of the electron cloud around the molecule creating temporary areas of lightly positive and negative charges

 When molecules come close together, the attractive forces between these positive and negative regions pull on the molecules and hold them together  The strength of the attraction depends on the size of the molecule, its shape, and its ability to attract electrons  Not as strong as covalent and ionic bonds  Ex: Allow water droplets to form