Atoms & Elements

• An atom is the smallest particle of a substance that can exist and still be that substance.
• Atoms are made up of protons, neutrons and electrons
• Neutrons have no charge
• Protons have a positive charge
• Electrons have a negative charge
• The mass number is the total number of protons and neutrons in an atom
• The mass number is equal to the total number of protons and neutrons in an atom
• The number of protons determines what element an atom is
• The atomic number is the number of protons in an atom
• Protons and neutrons are similar in mass, however electrons are much lighter (specifically 1/2000th lighter)
• A molecule is two or more atoms bonded together
• Electrons move around the nucleus in defined regions called shells
• The overall charge of an atom is neutral
• The number of protrons is equal to the number of electrons
• Elements are pure substances made up of only one type of atom
• There have been 118 elements discovered so far
• Each successive element differs by one proton
• Mass number - atomic number = number of neutrons
• Here is some information

  
• The mass of electrons is not included in the mass of an atom because it is so light it would not make a difference
• Isotopes are atoms of the same element that have different numbers of neutrons
• Isotopes have the same number of protons
• The first electron shell can hold 2 electrons
• The second electron shell can hold 8 electrons
• The third electron shell can hold 18 electrons
• The fourth electron shell can hold 32 electrons
• Electron shells fill up from inside to outside, starting with the first electron shell
• Elements in the periodic table are listed in order of increasing atomic number
• Ductile means not brittle
• Conductivity is how well an element conducts electricity or heat
• Malleable means able to be hammered into thin sheets without breaking
• The vertical columns on the periodic table are called groups and are numbered from 1-18
• Electrons found in the outermost shell are called valence electrons
• Elements in the same group tend to have similar chemical properties because of it's valence electrons
• For elements with 1-2 valence electrons, group number is equal to the number of valence electrons
• Rows in the periodic table are called periods
• Periods relate to the number of shells containing electrons
• For elements with 3-8 valence electrons, group number is equal to number of valence electrons + 10
• Group 1 on the periodic table are alkali metals
• Group 2 on the periodic table are alkaline earth metals