Chapter 2: Elements are the building blocks of matter

Chapter 2 – Elements are the building blocks of matter A pure substance that cannot be broken down or separated into simpler substances Made up of ONE kind of atom More than 115 elements known

Chemical Symbols Internationally recognized Consists of one or two letters First letter is always capitalized Second letter is always lowercase Some symbols are related to the English names of the chemical (e.g. Helium is He), but some are related to the latin names (e.g. Gold is Au – for Aurum)

Elements can be: metals, non-metals or metalloids

Metals, Non-metals & Metalloids Metals are: Shiny Malleable Ductile Usually solid Good conductors of heat and electricity

Metals, Non-metals & Metalloids Non-metals are: Gases or brittle solids Dull Non-malleable Non-ductile Poor conductors of heat and electricity

Metals, Non-metals & Metalloids Metalloids are: Solids Shiny or dull Non-malleable and non-ductile May conduct electricity Poor conductors of heat silicon arsenic

Chapter 2.2 - The Periodic Table and Chemical Properties Organizes the elements according to their physical and chemical properties The one we use was developed by Dmitri Mendeleev in 1867

Mendeleev’s Periodic Table Mendeleev’s two main contributions: He organized all the known elements according to properties and characteristics He recognized the need to leave spaces for elements not yet discovered

The Periodic Table Includes each element’s Name - Symbol Atomic number - Atomic mass

Some things to remember: Atomic Number = # of protons # protons = # electrons (neutral charge!) Atomic numbers increase one by one A carbon atom has 6 protons and 6 electrons!

Some things to remember: Atomic mass is the average mass of the atoms of an element (measured in amu) When you round the atomic mass, you get the mass number (which equals the number of protons and neutrons in an atom of an element) The atomic mass is 12.01 amu, so the mass number rounds to 12... So there are 12 protons and neutrons in total

Some things to remember: So the # of neutrons can be calculated by: mass number – # of protons (atomic #) = # neutrons The atomic mass /mass number tend to increase with the atomic number , but there are exceptions In a carbon atom, the number of neutrons: mass # - # protons = # neutrons 12 – 6 = 6 neutrons