Section 3

Atom: The basic unit of matter All matter is composed of atoms Atoms are microscopic particles It would take 4 million of the largest atoms to form a line 1 mm long Elements 1 of the 111 simplest substances from which more complex substances are made Each has a unique set of chemical and physical properties

What are some elements that you are familiar with? Aluminum Copper Oxygen Hydrogen Nitrogen What is the name of the table where we can find all of the elements? Periodic Table

The elements are distinguished on the Periodic Table by symbols O = Oxygen H = Hydrogen Li = Lithium Na = Sodium The symbols can be 1 – 3 letters 3 letter symbols are used for unnamed elements

A number of symbols are based on the Latin names for elements This was the language of many early chemists Sn is an abbreviation for stannum and the Latin word for tin Other elements have been named in the honor of a person or place where the element was discovered

How many known elements are there? 111 Which is the most common element? Hydrogen More than 90% of the atoms in the known universe are hydrogen atoms Oxygen & Silicon make up more than 70% of the mass of the Earth’s crust. Table 1-15

What four elements are living things primarily composed of? Carbon Hydrogen Oxygen Nitrogen These 4 chemicals combine to create thousands of different chemicals needed to sustain life. Figure 1-14 Table 1-6

Molecule: 2 or more atoms combined in a definite ratio Can be the same element or different elements N 2 gas is a molecule with 2 elements of Nitrogen joined together Monatomic gas: Individual atoms Figure 1-16a Diatomic gas: 2 or more atoms joined together Nitrogen gas Figure 1-16b

Allotrope: One of a number of different molecular or crystalline forms of an element Ex: Oxygen O 2 – the diatomic gas that we breathe O 3 – Ozone which is an allotrope with three oxygen atoms The properties of allotropes vary widely Oxygen: colorless, odorless gas essential to most forms of life Ozone: toxic, pale blue gas with a sharp odor

Carbon allotropes Graphite Diamond 60 carbon atom – buckminsterfullerene or buckyball Buckytube