Introduction to Chemistry

Ted-Ed: Search for the Atom History Early Greeks thought matter could be subdivided forever. ~ 450 B.C. Empedocles suggested all matter was made of only 4 “elements” earth, air, water, and fire ~ 400 B.C. Democritus suggested all matter was made of atoms, tiny particles that cannot be broken down further. He was not believed! Empedocles – Greek philospher – all 4 elements were indestructable and could combine to form different structures Democritus – everything is composed of atoms, space lies between atoms – smallest part of element that still remains element Hennig Brandt – German alchemist (study transformation of matter), discovered phosphorus by heating residues of boiled down urine, produced a liquid that solidified  phosphorus! Cavendish – first to discover hydrogen – lots of experiments yielded a “flammable gas” Experimenters such as Robert Boyle, Henry Cavendish and Antoine Lavoisier produced gases such as oxygen and hydrogen. Ted-Ed: Search for the Atom

John Dalton invented the modern atomic theory. Elements are all made up of extremely small particles called atoms. The atoms of each element are all identical, while atoms of different elements will have different properties. Each chemical compound is unique and consists of a particular combination of atoms. Chemical reactions involve the reshuffling of atoms in a compound to make new compounds. Dalton – English chemist Now we know atoms can be destroyed via nuclear reactions (not chemical reactions), atoms can be broken down into smaller parts – protons, neutrons, electrons Note: updates to Dalton’s original theory have been made as additional information was discovered.

Ted-Ed: What is the Universe Made Of? Pure substances A pure substance is a made up of only one type of particle. There are only two types of pure substances: Elements Compounds An element is a pure substance that cannot be separated into simpler substances by chemical processes. Compound – H20 – hydrogen and oxygen A compound is a pure substance that is composed of two or more different atoms combined in a specific way. Ted-Ed: What is the Universe Made Of?

Subatomic Composition of Atoms An atom is the smallest possible piece of an element which still has the properties of the element. A subatomic particle is any piece of an atom. Location Mass Charge protons neutrons electrons 1 amu ~ 0 amu + 1 -1 nucleus orbitals around nucleus Amu = atomic mass unit

Bohr Model of Atomic Structure Shows all electrons in each energy level around the atom. Atomic number = protons Oxygen At. # = 8 8 protons 8p Atomic mass = protons + neutrons 8n Oxygen mass = 16 8 neutrons Atomic number = protons Atomc mass – protons = neutrons -neutrons and protons for atoms w/ fewer than 30 protons  after that, more neutrons than protons because repulsion between protons makes it less stable and more neutrons keep the protons further apart Note: a neutral atom has no overall charge. protons (+) = electrons (-) Oxygen 8 protons = +8 8 electrons (-8)

Assignment In Class: Atomic Structure Worksheet Homework: Electron Configuration Worksheet (leave Lewis Diagram column blank)