CH 18 Chemistry Of Earth and The Known Universe Atomic Structure Subatomic Particles Proton- P+ positive charged - in nucleus Number of P+ distinguishes one atom from another Made of 2 up quarks (+2/3 charge) and 1 down quark (-1/3 charge) Neutron- No neutral charged - in nucleus Made of 2 down quarks and 1 up quark Electrons Electron- enegatively charged - swarming in energy levels around nucleus of atom (electron cloud). Electrons (e-) are attracted to the positively charged protons (P+) in the nucleus, helping them remain close to the nucleus in swarming levels. Energy Levels Electrons e- have a specific amount of energy when in each level. K – Shell has least energy M – Shell has most energy (as far as we’re going) e- can occupy only 1 level at a time No matter how many levels the outer level (valence) can have no more than 8 e Most stable atoms have 8 e- in valence 18.2 Comparing Atoms The number of P+ determines the type of atom. If you change the number of P+ you change the atom. 18.2 Atomic Number The Atomic Number is total number of protons in the nucleus of an atom. 18.2 Mass Number • The total number of protons and neutrons in the nucleus of an atom is called the Mass Number or Atomic Mass. 18.2 Isotopes Isotopes are atoms of the same element that have different numbers of neutrons. Each of the below atoms are hydrogen, but they are all isotopes of hydrogen. Isotopes • An atom can have 2 or more isotopes • Isotopes have different numbers of neutrons – Thus different mass numbers – More N add mass to atom – Heavier elements are radioactive (give off N) 18.3 The Periodic Table of Elements Elements are made up of only one kind of atom. Compounds are made up of combinations of atoms. Elements that are part of the same group act alike. 18.3 The Periodic Table of Elements Dimitri Mendeleev (18341907) organized information about all the known elements in a table that visually organized the similarities between them. Mendeleev placed each element on the table in a certain row and column based on its properties. The chemical symbol is an abbreviation of the element’s scientific name.