Elements and Life Basic chem. review

Elements and Compounds Organisms are made of Matter. Which is composed of elements. An element is a substance that cannot be broken down any further. (atoms) A compound is a substance consisting of two or more elements in a fixed ratio (molecules). Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Table 2-1

Fig. 2-4a (a) Nitrogen deficiency

Fig. 2-4b (b) Iodine deficiency

Second shell Third shell Hydrogen 1 H Lithium 3 Li Beryllium 4 Be Boron 5 B Carbon 6 C Nitrogen 7 N Oxygen 8 O Fluorine 9 F Neon 10 Ne Helium 2 He Atomic number Element symbol Electron- distribution diagram Atomic mass 2 He 4.00 First shell Sodium 11 Na Magnesium 12 Mg Aluminum 13 Al Silicon 14 Si Phosphorus 15 P Sulfur 16 S Chlorine 17 Cl Argon 18 Ar Electrons Electrons are found around the outside of the nucleus of atoms

Valence electrons are those in the outermost shell or energy level Atoms seek to have a full outer energy level. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Valence electrons

Bonding * Atoms bond so that their outer energy level will be full (contain 8 electrons, 2 for hydrogen) *

Covalent Bonding atoms combine by sharing electrons in their outer energy level (Water) - shared electrons move around both atoms. - covalent bonds produce molecules. Ex. Water Molecule (H 2 0)Water Molecule

Polar Covalent Bonds - a polar covalent bond occurs when electrons are shared unequally. The stronger atom’s nucleus pulls the electrons closer than the weaker atom’s. The strong atom becomes slightly negative, the weaker atom becomes slightly positive. (ex. water) Ex. Water(H 2 0) polarpolar + + -

Fig  – – ++ ++ H H O H2OH2O

Non-Polar Covalent Bonds - a non-polar covalent bond occurs when electrons are shared equally. (example oxygen gas) Ex. Chlorine gas(Cl 2 )

Ionic Bonding Ionic Bonding – a atoms combine by gaining or loosing electrons. (to get a full outer energy level) Ionic Bonding - the metal gives electrons to the non-metal and becomes positive (cation- a positive ion) -the non-metal accepts electrons from the metal and becomes negative (anion- a negative ion) - since they are oppositely charged, they stick together (bond) ex NaCl Goes to Cl Cl slightly negative Na slightly positive

Fig NaCl Na Cl Na Sodium atom Chlorine atom Cl Na + Sodium ion (a cation) Cl – Chloride ion (an anion) Sodium chloride (NaCl)