Chemistry
Pure Substances: type of matter, Can be separated into elements and compounds.
There are 2 types of pure substances: Elements can’t be broken down into other substances and contain only one kind of atom Compounds are substances made up of two or more different elements combined together
How are elements arranged?: Elements are arranged into columns (vertical) and rows (horizontal) according to reactivity and mass. These columns are referred to as groups, while the rows are called periods.
How does the arrangement of these elements work?: Reactivity decreases as you move left to right across each period. Mass increases as you move top-down through groups and also as you move from left to right across a period.
Group 1 - Alkali Metals: Very soft, Very reactive, Easily give an electron to form a compound, and Needs special storage.
Group 2 - Alkaline Earth Metals: Very reactive, though not as reactive as group 1 and they are not found freely in nature
Group 17 - Halogens: Non-metallic elements and the most reactive non-metals
Group 18 - Noble Gases: Most stable and un-reactive elements and has the Maximum number of electrons possible in their outer shell
Whats are the physical properties of Metals and Non-metals: metals are lustrous, good conductors, have high melting points, have high density, are malleable, are ductile, usually solid at room temperature, are opaque as thin sheet, and are sonorous. Non-metals are dull, poor conductors, non-ductile, brittle, maybe solid, liquid, or gas at room temperature, transparent as thin sheet, and are not sonorous.
What is atomic number: the number of electrons in a neutral atom or the number of protons in the nucleus.
What is atomic mass?: tells you the total mass of all the protons and neutrons in an atom. The number of neutrons can be determined by subtracting the atomic number from the atomic mass.
Whats an Ion: The gain or loss of electrons to form chemical bonds with other atoms.
What is it called when an atom gains an electron?: If an atom gains electrons, it becomes negatively charged and is referred to as an anion
What is it called when an atom loses an electron?: If an atom loses electrons, it becomes positively charged and is referred to as a cation
What is a compound?: A compound consists of two or more different elements bonded together.
What is a molecule?: A molecule consists of any two elements bonded together; elements can be the same, or they can be different.
What are diatomic elements?: Elements which always bond together in their pure form
Explain Chemical Formulas: Chemical formulas tell us which elements are present in a compound (the letters/alphabets), how many of each element is present (Subscript numbers after each letter), and what state of matter the compound is at room temperature (Subscript letters). Example : H2O(1/l)
Wha are the Two types of bonds: Ionic, which is when a non-metal and metal element bond together and Molecular/covalent, which is two non-metal elements bond.
What are the parts of an Atom?: Electrons - have a negative charge & orbit the nucleus extremely fast.
Nucleus - the dense center of the atom. Contains 99.9% of the atom’s mass.
Protons - have a positive charge. There are the same # of protons & electrons in a stable atom.
Neutrons - have no charge. Are in the nucleus with the protons.
What is alchemy?: The forerunner of chemistry, it was concerned with converting base metals into gold, not in understanding the nature of matter.
What is Democritus’s model?: “All matter is made up of tiny indivisible particles called atoms. And this model had no experimental evidence.
What is John Dalton’s Atomic Theory/Billiard ball model:
All matter is composed of tiny particles called atoms
Atoms of a given element are the same
Atoms cannot be divided, created, or destroyed
Atoms of different elements combine to form compounds.
In chemical reactions, atoms are separated, rearranged and combined
J.J Thomson model: Discovered the nucleus
Proposed the Plum Pudding Model, which includes:
“The atom is composed of negatively charged particles.”
He called these particles electrons.
Determined the very large charge to mass ratio of an electron
Ernest Rutherford: Gold foil Experiment.
Used radioactive alpha particles shot through gold foil.
Most particles passed straight through
Some were deflected
Conclusion; the atom is mostly empty space
Atom has a very dense, small, positively charged center, named the nucleus
Niels Bohr’s Model: Proposed a model where electrons travel around the nucleus in circular orbits.
The model is called the planetary or the electron orbit Model.
Electrons jump orbits by gaining or losing energy.
Quantum Mechanical Model: Mathematically describes the wave properties of electrons.
Developed by many Scientists.
Positive nucleus with a fuzzy cloud of electrons.
Electrons act as both waves and particles.