8th Grade An interlude for atoms

Contains only one type of atom Organized in Periodic Table Element Contains only one type of atom Organized in Periodic Table * 90 occur in nature * 114 in total. (Could this change?) Sure it could – as scientists discover more elements

Iron Gold Beryllium Phosphorus

Meet the Elements video - https://www.youtube.com/watch?v=Uy0m7jnyv6U

Atom – smallest unit of element that has properties of that element * Nucleus – made of protons (positive charge) & neutrons (no charge). - Has 99% of mass but only 1/100,000 of size. * Electron cloud – negative charge. Electrons can be anywhere in cloud Parts of an atom video - https://www.youtube.com/watch?v=lP57gEWcisY

Atomic Number = number of protons (also number of electrons). Why does the nucleus have a positive charge? Has protons which are positively charged. Atoms are neutral. Why? Protons are equal to electrons. Atomic Number = number of protons (also number of electrons). Mass Number = equal to the sum of protons & neutrons in nucleus.

the Periodic Table Page R12 and R13 in Dynamic Earth Book

p+ e- 8 16 19 39 92 142 13 14 Element Atomic Number Mass Oxygen Neutrons Oxygen 8 16 Potassium 19 39 Uranium 92 142 Aluminum 13 14

If the number of protons in 2 atoms is different then you have different elements. ex. 4 protons 5 protons beryllium boron If you have same number of protons in two substances but different neutrons, then you have the same elements but they are called isotopes.

Isotopes: have the same number of protons but different number of neutrons.

A has 24 protons & 25 neutrons. B has 24 protons & 26 neutrons. How are isotopes used? To treat some types of cancer Geologists use them to date some rocks & fossils. Problems: A has 24 protons & 25 neutrons. B has 24 protons & 26 neutrons. Are A & B different elements or isotopes? C has an atomic number of 12 & mass number of 24. D has an atomic number of 13 & a mass number of 26. Are C & D different elements or isotopes? Same element (Chromium) but isotopes Different elements (12 is Magnesium 13 is Aluminum)

Compounds Formed when atoms of more than one element combined. Properties of a compound are very different from properties of the elements that make it up. Ex. NaCl = salt Natural State Color Problems Na (sodium) Solid metal Silvery Explosive in water Cl (chlorine) Gas Greenish poisonous NaCl (salt) Solid crystal White OK

Atoms can gain or lose electrons This makes them ions Why is the overall charge of an uncharged atom zero? It has the same number of protons as electrons If a Hydrogen atom lost an electron, would it be positive or negative? Positive – there would be more protons than electrons H+ (hydrogen ion)

pH pH measures how acidic and basic something is Acids are 0-6 – have H+ ions (hydrogen ions) Examples? Bases are 8-14 – have OH- (hydroxide ions) 7 is neutral

Living things rely on their pH remaining constant Acid pH in body of water Acid rain