 Element – building block of matter  Atom – smallest unit of an element that contains all the properties of that element  117 known elements = 117 types of atoms  Atoms identified by number of protons  Empty space in atoms

 Smallest particles of matter: protons, neutrons, electrons  Protons – positive charge, located in nucleus  Electrons – negative charge, located in orbitals around nucleus, smaller than protons and neutrons  Neutrons – no electric charge, located in nucleus, same size as protons

 26 protons = iron atoms  Many atoms: protons = neutrons  Some atoms: protons < neutrons  Hydrogen: neutrons < protons  Electrons = protons  electrically neutral

 Mass is concentrated in nucleus (central core)  Nucleus contains protons, neutrons  Charge of nucleus = number of protons

 Located in space around nucleus – orbitals/electron clouds  Orbitals contain a maximum of 2 electrons  Half as many orbitals as electrons ▪ Calcium has 20 electrons and 10 orbitals  Constantly spin, but not in a fixed pattern, anywhere in the orbital

 Buffers between protons (same charges repel)  Hold nucleus together  Number can vary as long as there is at least the same number of neutrons as protons  Isotopes – atoms of the same element with different number of neutrons  Carbon – 6 protons; may have 6, 7, or 8 neutrons

 1. false  2. true  3. true  4. false  B. Air is made up of particles and takes up space. There is oxygen in air, and oxygen is an element, which means it must be made of matter.  C. B

 A. protons, neutrons, electrons  B 1. false  2. false  3. true  4. true

 A1. empty space  2. in the nucleus  3. a maximum of two electrons  B. electron is to orbital

 A 1. 1, 0, 1  2. 2, 2, 2  3. 3, 4, 3  4. 6, 6, 6  B. It only has one proton, so there are no other positive charges to repel it.