Chemistry

The emergence of biological function starts at the chemical level ATOMS AND MOLECULES The emergence of biological function starts at the chemical level Everything an organism is and does depends on chemistry Chemistry is in turn dependent on the arrangement of atoms in molecules

Biological Hierarchy Each level in the hierarchy builds on the one below it. Atoms and ecosystems are at opposite ends of the hierarchy

Biological Hierarchy

Life requires about 25 chemical elements A chemical element is a substance that cannot be broken down to other substances by ordinary chemical means 25 chemical elements are essential to life 4 MAIN ELEMENTS:

Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter, but there are other elements necessary for life

Elements can combine to form COMPOUNDS H2O NaCl

The smallest part of an element is an atom Atoms consist of protons, neutrons and electrons Protons positively charged 2 Protons Nucleus Neutrons electrically neutral 2 Neutrons Electrons negatively charged 2 Electrons

Elements consist of ONE type of atom Atomic Number = # of Protons AND also # of Electrons Meet the Elements 8 protons 8 electrons 1 proton 1 electron

Isotopes Nonradioactive carbon-12 Nonradioactive carbon-13 Radioactive carbon-14 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 7 neutrons 6 electrons 6 protons 8 neutrons Isotopes are atoms of the same element that differ in number of neutrons

Electrons arrangement determines the chemical properties of an atom Electrons are arranged in energy levels The outermost level determines the chemical properties of an atom

Atoms are like onions…

Octet Rule Level One: 2 electrons Level Two: 8 Electrons Level Three: 18 Electrons HOWEVER Level 3 can hold a maximum of 18, but needs at least 8 electrons to be STABLE

Valence Electrons Valence electrons are the electrons AVAILABLE for bonding Valence electrons = electrons on outermost level Worksheet C 6 H 1 O 8 Ar 18

Number of Electrons needed for stability Element Symbol Atomic Number Mass Number Number of Protons Number of Neutrons Number of Electrons Valence Electrons Number of Electrons needed for stability Hydrogen 1 Oxygen 8 Nitrogen 7 Carbon 12 Phosphorus 31 Chlorine 18

Atoms whose outermost energy levels are not full tend to interact with other atoms and gain, lose or share electrons Outermost energy level (can hold 8 electrons) Electron First energy level (can hold 2 electrons) HYDROGEN (H) Atomic number = 1 CARBON (C) Atomic number = 6 NITROGEN (N) Atomic number = 7 OXYGEN (O) Atomic number = 8

Ionic Bonding Protons +11 Protons +17 Electrons -11 Electrons -17 Charge 0 Protons +17 Electrons -17 Charge 0

Ionic Bonding = Transfer of Electrons When atoms gain or lose electrons, charged atoms called ions are created An electrical attraction between ions with opposite charges results in an ionic bond Protons +17 Electrons -18 Charge -1 Protons +11 Electrons -10 Charge +1 Na+ Sodium ion Na Sodium atom Cl Chlorine atom Cl– Chloride ion Sodium chloride (NaCl)

Sodium and chloride ions bond to form sodium chloride, table salt Na+ IONIC BONDING = IONIC COMPOUNDS Cl–

What about these atoms?! Covalent Bond

Covalent Bonding Some atoms share outer energy level electrons with other atoms, forming a covalent bond Atoms joined together by covalent bonds = molecules Practice NH3, CO2

**Lewis Dot Structure: include only valence electrons

Covalent vs. Ionic Bonding

Molecules can be represented in many different ways Lewis Dot Structure

Let’s Practice BEST SONG EVER