10th Grade Chemistry

• Isotopes are elements which have same number of protons but different number of neutrons.
• Isotopes share similar chemical properties but have different physical properties.
• Endothermic: A reaction in which energy is absorbed to break bonds. This feels cold and the value of enthalpy change is positive.
• Exothermic: A reaction in which energy is released to form bonds. This feels hot and the value of enthalpy change is negative.
• Covalent bonding occurs generally between non-metals sharing a pair of electrons and a positively charged nuclei
• Cations are positively charged ions
• Anions are negatively charged ions
• Noble gases are stable and extremely unreactive because they have a full valence shell.
• Ionic bonding occurs through the electrostatic attraction between oppositely charged metal and non-metal ions.

  
• The octet rule states that elements will try to achieve a stable electron configuration by having 8 electrons in their valence shell.
• Why is the mass of electrons not counted in the mass number?

  Because the mass of electrons is negligible.
• △ Exceptions!

  Some elements do not obey the octet rule such as hydrogen with its duet rule or boron & aluminum with its sextet rule.
• Metallic bonding occurs through the strong electrostatic attraction between delocalized electrons and a lattice of cations

  
• Alloys are less malleable than their base metal.