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E2 – E35. Atoms, Elements & Compounds. Atoms. An atom is the smallest unit of a pure substance that still has the properties of that substance. Parts of an Atom. Nucleus – the center of an atom, it has a positive electric charge. Every nucleus has at least one proton.
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E2 – E35 Atoms, Elements & Compounds
Atoms • An atom is the smallest unit of a pure substance that still has the properties of that substance.
Parts of an Atom • Nucleus – the center of an atom, it has a positive electric charge. Every nucleus has at least one proton. • Proton – a subatomic particle that has a positive electric charge. • Neutron – a subatomic particle that has no electric charge. (neutral) • Electron – a subatomic particle with a negative electric charge.
The Nucleus • The nucleus is a very dense region of an atom, made of protons and neutrons, at the center of an atom. The electrons circle the nucleus.
Atomic Number • The atomic number of an atom is determined by the number of protons in the nucleus. • Oxygen #8 Hydrogen #1
Element • An element is a pure substance that’s made up of only one kind of atom. It cannot be broken down into other substances by ordinary laboratory methods.
Types of elements • Metal – an element that conducts heat and electricity well. 75% of elements are metals. Metals are shiny. • Nonmetals – do not conduct electricity, and they are not shiny or malleable. • Malleable means that metal can be bent and rolled into sheets.
Periodic Table of Elements • Elements are arranged by their atomic number (protons in the nucleus). • Each square is an element. • The square contains the atomic number, chemical symbol, name, and atomic mass. • Elements are solids, liquids, and gases. • Families are in columns and have similar characteristics.
Molecules • Atoms often bond together and form larger units. • Molecules are units formed from two or more atoms. • Oxygen = two bonded oxygen atoms • Carbon Dioxide= one atom of carbon and two atoms of oxygen • The electrons circling the nucleus join together to form the bond.
States of Matter • Solid- a definite shape and volume, molecules are held tightly in place. • Liquid – definite volume, but no definite shape, molecules are far apart • Gas – no definite shape or volume, molecules move around freely • Adding or taking away heat creates the changes of state.
Plasma • Plasma is a gas with ‘free’ electrons. • The core of a fire and the stars in the sky are both examples of plasma.
Atomic Progression • Atoms become elements. • Elements become molecules. • Molecules become Compounds.
Compounds • A compound is a substance formed from the atoms of two or more elements. • Water - H2O • Table Salt – NaCl • Rust – Fe2O3 • Sugar – C12H22O11
Acids & Bases • An acid is a compound that reacts easily with other substances, and turns litmus paper red. They are very corrosive and can destroy body tissue. • A base is a compound that also reacts easily with other substances, but turns litmus paper blue. They are slippery and have a bitter taste. • Litmus paper is a small strip of paper inserted into a substance to test it’s acidity.
pH Scale • The strength of an acid or base is measured on the pH scale. • pH 7 is neutral • pH 0-7 are acids • pH 7-14 are bases
Important Scientists • John Dalton – In the early 1800’s he determined that everything is made of atoms. • J.J. Thomson –1900 - there a negative electrons scattered in a positive sphere • Ernest Rutherford – 1911 - an atom is mostly empty space with a tiny nucleus. • Niels Bohr – 1913 - electrons move in ‘energy orbits’ around the nucleus
Cool Information • Atomic Number = Number of Protons • Atomic Number = Number of Electrons • Number of Neutrons = Rounded Atomic Mass – Atomic Number • You must be able to look up the atomic mass, then round it!
