Science 14: Chapter #2 - Pure Substances. Baier Science 14

Transcription

1 Science 14: Chapter #2 - Pure Substances

2 A) The Periodic Table By the 1860 s scientists had discovered 64 elements and had recorded many of their properties. Elements are substances that can t be broken down into other substances and contain only one kind of particle (atom).

3 A) The Periodic Table In 1869, Dmitri Mendeleev wrote down all the properties for each know element on a file card. He then began to organize them according to their properties. All the elements with similar properties were organized into groups Next he organized the elements within each group from lightest (on the left) to heaviest (on the right). Mendeleev noticed that some elements were missing. He predicted that these elements had not yet been discovered. Mendeleev s work provided the basis for today s modern Periodic Table.

4 Periodic Table of the Elements

5 A) The Periodic Table A periodic table is a chart on which scientists have organized all of the elements. The elements in the periodic table are made up of atoms. Atoms are the smallest bits of matter. Ex. Water is made up of two atoms of hydrogen for every one atom of oxygen. Since the times of Mendeleev scientists have discovered 112 elements, many of which Mendeleev predicted.

6 B) Patterns and Trends The elements in the periodic table are arranged in columns and rows so that elements with similar properties appear close together. The columns are referred to as groups. Elements in groups are arranged according to their physical and chemical properties. The rows are referred to as periods. Elements in periods are arranged in order of increasing mass.

7 C) Metals and Non-Metals The staircase on the periodic table separates the metallic elements on the left from the nonmetallic elements on the right. The differently coloured squares between the metals and the non-metals show metalloids. These elements exhibit some of the properties of metals and some of the properties of non-metals.

8 C) Metals and Non-Metals

9 Metals Bright metallic shine (luster) Easily shaped (malleable) Solids (except mercury) Non-Metals Dull, various colours Brittle Solid or gas (except bromine which is a liquid) Good conductors of heat and electricity Poor conductors of electricity and heat

10 2.2 Elements and Compounds

11 2.2 Elements and Compounds A substance made up of two or more different elements combined together is known as a compound. Pure substances can be made up of one kind of element or one kind of compound (a combination of elements) Oxygen is a pure substance consisting of a single element. Distilled water is a compound consisting of the chemical joined elements of hydrogen and oxygen.

12 2.2 Elements and Compounds An element is a pure substance that can t be broken down into simpler substances. Compounds can be broken apart into simpler substances. This is done through a process called a decomposition reaction.

13 2.3 Chemical Names and Formulas In 1919, a group of chemists formed the International Union of Pure and Applied Chemistry (IUPAC). These chemists established an international standard for chemical symbols and names. A) Element symbols are either one or two letters. Case 1: First letter of the elements name is used Example: C for Carbon or N for Nitrogen Case 2: Once scientists ran out of letters, they began to use the first and a second letter from the element name. Example: Ca for Calcium or Zn for Zinc. Case 3: For those elements which bear Greek or Latin names, the symbols is based on the historic name. Example: Pb for lead, which in Latin is plumbum.

14 B) Chemical Formulas A chemical formula represents a compound. They are made up of letter and numbers. Letters tell you which elements are in the compound Subscript numbers tell you the proportion of the elements contained. A letter in brackets after the compound tells you what state it is in (solid, liquid, gas or aqueous)

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