1. 2.1 Atoms, Ions, and Molecules KEY CONCEPT All living things are based on atoms and their interactions.

2. 2.1 Atoms, Ions, and Molecules Chemistry – the study of matter and its changes Matter – anything that has mass and takes up space –Element – one particular type of atom -Differs in the number of protons they have –Chemical symbol – abbreviated way of representing each type of element (or atom) –Periodic Table of the Elements - Periods – across rows on table -Groups or Families – up and down columns on table -Atomic number – listed on table, tells number of protons -Average Atomic mass – listed on table, protons plus neutrons -Valence electrons – how many electrons in outer shell and ready for interactions

3. 2.1 Atoms, Ions, and Molecules Living things consist of atoms of different elements. An atom is the smallest basic unit of matter. An element is one type of atom. H O Hydrogen atom (H) Oxygen atom (O)

4. 2.1 Atoms, Ions, and Molecules –The nucleus has protons and neutrons. –Electrons are in energy levels outside nucleus. Oxygen atom (O) Nucleus: 8 protons (+) 8 neutrons outermost energy level: 6 electrons (-) inner energy level: 2 electrons (-) An atom has a nucleus and electrons.

5. 2.1 Atoms, Ions, and Molecules Chemical formula –Abbreviated way to communicate the ratio of each type of atom in a compound or molecule -Examples: Chemical bond – force holding one atom to another within a compound or molecule –Covalent bonds – share electrons -Example: –Ionic bonds – transfer electrons -Examples:

6. 2.1 Atoms, Ions, and Molecules –water (H 2 O) O HH _ ++ A compound is made of atoms of different elements bonded together.

7. 2.1 Atoms, Ions, and Molecules –carbon dioxide (CO 2 ) A compound is made of atoms of different elements bonded together. –water (H 2 O)

8. 2.1 Atoms, Ions, and Molecules –many other carbon-based compounds in living things A compound is made of atoms of different elements bonded together. –water (H 2 O) –carbon dioxide (CO 2 )

9. 2.1 Atoms, Ions, and Molecules Ions form when atoms gain or lose electrons. An ion is an atom that has gained or lost one or more electrons. The electrons have been transferred! –positive ions –negative ions Ionic bonds form between oppositely charged ions. Sodium atom (Na)Chlorine atom (CI)Sodium ion (Na + )Chloride ion (CI - ) Na loses an electron to CI ionic bond gained electron

10. 2.1 Atoms, Ions, and Molecules Atoms share pairs of electrons in covalent bonds. A covalent bond forms when atoms share a pair or pairs of electrons. covalent bonds Oxygen atom (O) Carbon atom (C) Oxygen atom (O) Carbon dioxide (CO 2 ) –Single covalent bonds –Double covalent bonds –Triple covalent bonds