10/3/14 Objective: What are elements, compounds, and atoms? Do Now: Give an example of “matter.” Chapter 4: The Chemical Basis of Life

Matter: Anything that occupies space and has mass Element: Pure substance that cannot be broken down into other substances Ex: Carbon (C), Hydrogen (H), Gold (Au) 4 most common elements in living matter (96% of our body): carbon (C), oxygen (O), hydrogen (H), nitrogen (N)

Trace Element: elements that make up less than 0.01 percent of your body, but are critical to life Ex: iron Compound: 2 or more elements chemically combined Ex. Carbon dioxide(CO 2 ), water(H 2 O)

Atoms atom: smallest possible particle of an element Made up of : Nucleus: central core of atom that contains protons: single unit of positive electrical charge (+) neutrons: electrically neutral = no charge Electrons: single unit of negative electrical charge (-) located outside of the nucleus Why do you think the electrons remain close to the nucleus? Atomic number: number of protons in an atom –Differentiates elements

Carbon Potassium Atomic Weight (Mass number): # of protons + # of neutrons

Isotopes Isotope: same number of protons but different number of neutrons –Can make an element radioactive – ex: 12 C = normal, 14 C =radioactive Radioactive Isotope: nucleus decays over time giving off radiation in the form of matter and energy – ex. Carbon dating

Energy Levels The electrons in an atom determine how it will react with other atoms Electrons are found in clouds outside the nucleus Energy Levels –First level = lowest, nearest to nucleus can hold 2 electrons – Second level = can hold 8 electrons –Most reactive when they have partially full energy levels Nitrogen

Chemically reactive or Inert (doesn’t react)?