Elements, Atoms, Ions

The Elements

What elements do you think are most abundant in human body?

Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Magnesium

Do you know chemical formulas for any compounds?

H 2 0 CO 2 NaCl ???

What do you know about the atom?

What are electrons?

What are protons?

What are neutrons?

The Periodic Table  What does “Periodic” mean  What does the periodic table tell us?

Name an element that is normally a liquid, one that is normally a solid and one that is normally a gas Liquid: Mercury, Bromine Solid: Sulfur, Carbon, Iron, Copper ….

Gas: Oxygen, Nitrogen, Hydrogen, Helium …

Elements  Earth – about 88 elements occur naturally  These elements combine to form all of the compounds on our planet  Known elements (including man-made) number around 115 (scientists always working on producing more)  Chemists use standard names and symbols for elements. You will need to learn to write and recognize the most common.

You will be responsible for knowing names and symbols of the following: Oxygen (O) Hydrogen (H) Potassium (K) Chlorine (Cl) Fluorine (F) Iodine (I) Silicon (Si) Calcium (Ca) Gold (Au) Helium (He) Aluminum (Al) Carbon (C) Iron (Fe) Lithium (Li) Sodium (Na) Boron (B) Magnesium (Mg) Nitrogen (N) Sulfur (S) Bromine (Br) Phosphorus (P) Manganese (Mn) Barium (Ba) Platinum (Pt) Silver (Ag) Neon (Ne) Zinc (Zn) Lead (Pb) Copper (Cu) Mercury (Hg)

What do we mean by “Element”?

 Microscopic form – single atom of an element, e.g. H, C, F, W  Microscopic form – molecule made up of atoms of one element (H 2 , O 2 , S 8 )  Macroscopic form - Sample of element large enough to weigh  Generic form – referring to the atoms of element in various forms and combinations (e.g. the human body contains a lot of the element Oxygen)

John Dalton – early 1800s

Dalton’s Atomic Theory  Elements are made of tiny particles called atoms  All atoms of a given element are identical  The atoms of a given element are different form those of any other element  Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms  Atoms are indivisible in chemical processes. They are not created or destroyed in a chemical process. A chemical reaction simply changes the way atoms are grouped together.

Law of Constant Composition  A given compound always contains the same proportions of the elements. It doesn’t matter where the sample of the compound comes from.

 Water always contains 8g of Oxygen for every 1g of Hydrogen  Carbon Dioxide always contains 2.7g for every 1g of Carbon  Dalton’s atomic theory helped explain the law of constant composition  A pair of elements could combine in more than one way  NO   NO 2 N 2 O

Formulas of Compound  A compound is substance that is composed of the atoms or two or more elements.

 A compound always contains same relative numbers of atoms of each element (e.g. water always has 2 hydrogens and 1 oxygen)  Chemical formulas – atoms are indicated by the element symbols; number of each atom is indicated by a subscript – a number that appears to the right of and below the symbol for the element   NH 3 H 2 O 2 CH 4 C 6 H 12 O 6

When only one element in the compound, you don’t write the 1 as a subscript

Try to write some chemical formulas A compound with 2 Nitrogens and 5 Oxygens  N 2 O 5 A compound with 3 Carbons and 8 Hydrogens • C 3 H 8

Write the chemical formula for the following compounds:  A molecule that contains four phosphorous atoms and ten oxygen atoms  P 4 O 10 A molecule that contains one uranium atom and six fluorine atoms  UF 6 A compound that contains one aluminum atom for every three chlorine atoms AlCl 3