Elements, Compounds and Molecules Section 5.3. Free powerpoint template: 2 In total, 117 elements have been observed as of 2008, of

Elements, Compounds and Molecules

Section 5.3

Free powerpoint template: www.brainybetty.com2

• In total, 117 elements have been observed as of 2008, of which 92 occur naturally on Earth – the others are man-made!

• Every kind of matter has to be made up of one or more of these 117 elements.


• Matter that is made up of only one type of atom is called an element (like those on the periodic table)

• The atoms of any one element are exactly alike but the atoms of any given element are different from atoms of every other element:– Example:

• All hydrogen atoms are the same as all other hydrogen atoms but they are not the same as oxygen atoms


• Most of the substances we know are made up of two or more elements:– Water (H2O), salt (NaCl), carbon dioxide,

(CO2) and baking soda (NaHCO3)

• These substances are possible because atoms of different elements can link-up

• Elements are pure substances that cannot be broken down into simpler parts by ordinary chemical means

• Elements combine to produce compounds


• Some common elements are gold (Au), copper (Cu), hydrogen (H), oxygen (O)

• Most elements are found in a solid state but they can also be gasses and liquids (there are only 2 liquids)


• A compound is a substance made up of two or more elements

• When elements combine to make compounds they lose their own properties; the new compound has it’s own properties

• Compounds don’t have to be in the same state as the elements from which they are made

• Example: – hydrogen (gas) and oxygen (gas) make water (liquid)


Molecules

• A molecule is the smallest part of a compound that still has the properties of the compound

• It must have at least two atoms but can have thousands.

Atomic Theory

Explaining Chemical Facts and Laws


Dalton’s Atomic Theory

• All matter is made up of small particles called atoms• Atoms cannot be created, destroyed or divided into

smaller particles• All atoms of the same element are identical in mass

and size, but they are different in mass and size from the atoms of other elements

• Compounds are created when atoms of different elements link together in definite proportions


• Dalton’s model uses the idea that elements are different because their “particles” are different


Laws vs. Theories

• In science:– Laws do not explain anything, they just

describe and summarize– Theories explain why something happens


Atomic Masses

• Atomic mass is the mass of an average atom of an element

• Hydrogen was the lightest known element at the time so Dalton gave it an atomic mass of 1


• Since the atomic mass of Hydrogen was 1 Dalton theorized that all other atomic masses could be compared to the mass of Hydrogen.

• For example, the mass of Lithium is 3 so it is 3 times larger than Hydrogen etc.


• In Dalton’s New System of Chemical Philosophy, published in 1808, Dalton provided relative masses for 20 elements to support his atomic theory.

• He also showed 17 examples of how the theory explained the formation of compounds by proving that H2O has an atomic mass of 10

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Elements, Compounds and Molecules Section 5.3. Free powerpoint template: 2 In total, 117 elements have been observed as of 2008, of