Elements and Compounds |
Key Concepts
- Elements and Compounds are pure substances.
- An element is a pure substance that cannot be decomposed into simpler substances.
- Elements are listed in the Periodic Table of the Elements.
- Each element has a 1 or 2 letter symbol.
- A compound is a pure substance that can be decomposed into simpler substances.
- Compounds are made up of two or more elements.
Elements
An element is a pure substance that cannot be decomposed (broken down) into simpler substances.
| There are 92 naturally occurring elements.
Each element has been given a 1 or 2 letter symbol:
- the first letter of the symbol is always a capital letter
eg, H for hydrogen, C for carbon, N for nitrogen
- if there is a second letter in the symbol it is a lower case letter
eg, He for helium, Ca for calcium, Ne for neon
Elements can be present in nature as solids, liquids or gases.
| Liquid Elements |
Gaseous Elements |
Solid elements |
|---|
| 2 elements exist in nature as liquids: |
11 elements exist in nature as gases: |
all other elements exist in nature as solids, eg: |
mercury (Hg)
bromine (Br) |
hydrogen (H)
helium (He)
nitrogen (N)
oxygen (O)
fluorine (F)
neon (Ne)
chlorine (Cl)
argon (Ar)
krypton (Kr)
xenon (Xe)
radon (Rn) |
lithium (Li)
carbon (C)
sodium (Na)
magnesium (Mg)
aluminium (Al)
silicon (Si)
phosphorus (P)
sulfur (S)
potassium (K)
calcium (Ca)
zinc (Zn) |
The atmosphere is mostly made up of the elements nitrogen (~78%) and oxygen (~21%).
Common elements found in the earth's crust are:
- oxygen (O)
- silicon (Si)
- aluminium (Al)
- iron (Fe)
- calcium (Ca)
- sodium (Na)
- potassium (K)
- magnesium (Mg)
- hydrogen (H)
The most common elements found in living things are:
- carbon (C)
- hydrogen (H)
- oxygen (O)
- nitrogen (N)
- phosphorus (P)
- sulfur (S)
The most common elements found in the universe are:
- hydrogen (H)
- helium (He)
- oxygen (O)
- carbon (C)
|
| Some Elements |
|---|
| Name |
Symbol |
|---|
| hydrogen |
H |
| helium |
He |
| lithium |
Li |
| beryllium |
Be |
| boron |
B |
| carbon |
C |
| nitrogen |
N |
| oxygen |
O |
| fluorine |
F |
| neon |
Ne |
| sodium |
Na |
| magnesium |
Mg |
| aluminium |
Al |
| silicon |
Si |
| phosphorus |
P |
| sulfur |
S |
| chlorine |
Cl |
| argon |
Ar |
| potassium |
K |
| calcium |
Ca |
| scandium |
Sc |
| titanium |
Ti |
| vanadium |
V |
| chromium |
Cr |
| manganese |
Mn |
| iron |
Fe |
| cobalt |
Co |
| nickel |
Ni |
| copper |
Cu |
| zinc |
Zn |
| gallium |
Ga |
| germanium |
Ge |
| arsenic |
As |
| selenium |
Se |
| bromine |
Br |
| krypton |
Kr |
| rubidium |
Rb |
| strontium |
Sr |
| zirconium |
Zr |
| silver |
Ag |
| tin |
Sn |
| barium |
Ba |
| tungsten |
W |
| platinum |
Pt |
| gold |
Au |
| mercury |
Hg |
| lead |
Pb |
| uranium |
U |
|
Compounds
Compounds are pure substances made up of 2 or more elements.
Each compound has a formula showing which elements are present in the compound
Examples of some common compounds are shown below.
| compound name |
compound formula |
elements present |
|---|
| water | H2O | hydrogen (H) and oxygen (O) |
| ammonia | NH3 | nitrogen (N) and hydrogen (H) |
| carbon monoxide | CO | carbon (C) and oxygen (O) |
| carbon dioxide | CO2 | carbon (C) and oxygen (O) |
| sodium chloride | NaCl | sodium (Na) and chlorine (Cl) |
| sodium hydroxide | NaOH | sodium (Na), oxygen (O) and hydrogen (H) |
| calcium chloride | CaCl2 | calcium (Ca) and chlorine (Cl) |
| calcium carbonate | CaCO3 | calcium (Ca), carbon (C) and oxygen (O) |
| calcium nitrate | Ca(NO3)2 | calcium (Ca), nitrogen (N) and oxygen (O) |
| calcium phosphate | Ca3(PO4)2 | calcium (Ca), phosphorus (P) and oxygen (O) |
| calcium sulfate | CaSO4 | calcium (Ca), sulfur (S) and oxygen (O) |
| methane | CH4 | carbon (C) and hyrogen (H) |
| ethanol | C2H5OH | carbon (C), hydrogen (H) and oxygen (O) |
A compound can be decomposed into simpler pure substances.
For example, an electric current can be passed through water to form the elements hydrogen and oxygen.
Water can be decomposed into hydrogen and oxygen.
Water is a compound made up of hydrogen and oxygen.
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