| A | B |
|---|
| Ninety-two | elements occur naturally |
| Marie Curie | 1867 - 1934 |
| Pierre and Marie Curie discovered | the element radium |
| Marie Curie named the element | polonium after her native Poland |
| Hydrogen is a colourless, odourless | tasteless and highly flammable gas |
| Humans are 65% | oxygen |
| Humans are 18% | carbon |
| Humans are 10% | hydrogen |
| Humans are 3% | nitrogen |
| Humans are 2% | calcium |
| Sodium, a shiny metal, is | very soft |
| Chlorine is a | pale yellow-green gas |
| Mercury is the only metal | liquid at room temperature |
| Galena is an important ore of | silver |
| Silicon is the second most common | element in the Earth's crust |
| A semiconductor is a poor conductor | of electricity at low temperatures |
| A semiconductor is a good condutor | of electricity at high temperatures |
| Graphite is a form of | carbon |
| Dmitri Mendeleev | Russian teacher and chemist |
| Harriet Brooks | 1876 - 1933 |
| F, Cl, Br, I, At | Halogens |
| He, Ne, Ar, Kr, Xe, Rn | Noble Gases |
| The number of electrons in an atom | is always equal to the number of protons |
| Electrons in the outermost shell | are called valence electrons |
