| atomic radius decreases across a period why? | because the increasingly positive nuclear charge pulls the electrons in the outer shell closer to the nucleus. |
| The atomic radii can be determined from their van der Waals' radius. How can this be done? | Found by measuring the distance between the nuclei of 2 neighbouring, touching atoms which are not chemically bonded together. This distance is divided by 2 to give the van der Waals' radius. Figure will be higher that the single covalent radius of any given element. |
| Why are negatively charged ions larger than their original atoms. | Because each atom will have gained one or more extra electrons into their 3rd principle quantum shell. This increases the repulsion between its electrons, while the nuclear charge remains constant. This increases the size of any anoin compared with its atom |
| What does a change in melting point across a period reflect | Type of structure and bonding |
| Why is there a general increase in first ionisation energy across a period | because the increasing nuclear charge and decreasing atomic radius makes the attractive forces between the nucleus and outer electrons greater |
| Why does the maximum oxidation number of each element rises as we cross the period? (Period 3) | because the Period 3 element in each oxide can use all the electrons in its outermost shell in bonding to oxygen |
| Magnesium oxide and magnesium hydroxide are commonly used in what , and why? | indigestion remedies. Basic compounds neutralise excess acid in stomach, relieving pain |
| Compounds that can act as both acids and bases, are called ... | amphoteric |
| What is electronegativity? | power of an atom to attract the electrons in a covalent bond towards itself |
| Oxidation numbers rises as we cross Period 3, until we reach sulfur in Group 16, why? | Because Period 3 elements from sodium to phosphorus use all the electrons in their outermost shell, their valence electrons, in bonding to chlorine |
