Unit 3 Elements , Atoms, and Ions (Oh My!)

1. Unit 3Elements, Atoms, and Ions (Oh My!) Chpt 3 Elements, Atoms, and Ions Chpt 11 Modern Atomic Theory

2. Alchemical History • In ancient times, it was believed that there were only 4 elements: earth, wind, fire, water • https://www.youtube.com/watch?v=Gs069dndIYk • In the middle ages, alchemists attempted to create gold, the philosopher’s stone, or the elixir of life from natural materials. • Dangerous “experiments” • Recorded “symbols” of elements

3. What are elements? • Elements are made of one type of atom • Presently, there are 118 (both naturally occurring and man-made) and most are metals • Synthetic elements (>93) have very short lifespans from days to seconds • Little known facts: • the first element made after the Big Bang was hydrogen, which is also the most abundant in the universe • oxygen is the most abundant in the earth and the body • all living forms of matter (organic molecules) are made of carbon

4. Natural States of Elements • Most elements exist in their “pure elemental” form as a collection of single atoms • 7 elements exists as diatomicmolecules in their natural state • hydrogen, H2 - chlorine, Cl2 • nitrogen, N2 - bromine, Br2 • oxygen, O2 - iodine, I2 • fluorine, F2

5. Element Name and Symbols • Elements are named after their physical properties, scientists, countries/place • Rules for symbols • Always capitalize the first letter • some symbols come from their original Greek, Latin name

6. Chemical formulas for molecules and compounds • Formulas are shorthand for the name of the molec/cmpd • Represents the number of atoms for each element in the cmpd • H2O = 2 hydrogen atoms, 1 oxygen atom • C6H12O6 = 6 carbon atoms, 12 hydrogen, 6 oxygen atoms • ALWAYS use subscripts for the number • “1” is implied – do not write it

7. History of atomic theory • Law of Constant Composition – compounds always have the same ratios of elements regardless of their source • H2O = 2:1 • H2O2 = 2:2 = 1:1 • CO2 = 1 : 2

8. Dalton’s Atomic Theory (DAT) LoCC made John Dalton think about what made up elements…. • Elements are made of atoms. • All atoms of a given element are identical. • Atoms of a given element are different from those of any other element. • Atoms of one element can combine with atoms of other elements to form compounds. • Atoms cannot be separated by any means.

9. Thomson and the Plum Pudding Model 1897 – J.J. Thomson discovered the electron Used a cathode ray tube It proved that atoms are made of negatively charged particles, which he called “electrons”. Their negative charge was balanced by the overall positive charge of the atom. This made the whole atom neutral made of empty space. Plum Pudding (or chocolate chip cookie)

10. Ernest Rutherford and Gold Foil Experiment • Early 1900s Ernest Rutherford (and Co.) discovered the proton • Gold foil experiment • It proved that atoms contained a center of positive charge, which he called the “nucleus” filled with “protons”, or positively charged particles. The nucleus was surrounded by electrons.

11. Neils Bohr model • 1915 Neils Bohr theorized that electrons travel on orbits around the nucleus. The orbits have specific amounts of energy, or quantized energy. Electrons can jump orbits by absorbing or emitting energy. When electrons emit energy, they throw out a photon, or light particle.

12. Ground state electron – lowest energy level • Excited electron – higher energy level • As an excited electron falls back down to its ground state, it emits a photo

13. James Chadwick • 1920s, James Chadwick discovered the neutron • Bombarding heavy particles at atoms • It proved that atoms contained neutral particles in addition to protons and electrons. It accounted for the rest of the atom’s mass.

14. Atomic Structure Summary • Made of mostly empty space with a nucleus at center • Atoms contain 3 subatomic particles: • protons – positive charge, located in nucleus • neutrons – no charge, located in nucleus • electrons – negative charge, move around nucleus • Protons and neutrons make up the atom’s mass (atomic mass) • Number of protons identify the atom (atomic number) • A neutral atom has the same number of protons and electrons

15. Isotopes • Not all atoms of a particular element are identical • Isotopes – atoms of a given element that have a different atomic mass (different number of neutrons) • For carbon • C-12 (6 protons, 6 neutrons) • C-13 (6 protons, 7 neutrons) • C-14 (6 protons, 8 neutrons) • Use AZX notation • A – atomic mass • Z – atomic number • X – chemical symbol

16. Ions • When atoms lose or gain electrons, they become charged, called ions • Ions can be positive (+) or negative (-) • Cations are positive ions, electrons lost • Anions are negative ions, electrons gained