Focus on Valence Electrons: Draw valence for Na and Cl: NaCl What will happen when the two elements are combined? Na will transfer 1 electron to Cl Now, both atoms have full valence! Na +1 Cl -1 Opposite charges attract and ionic bond forms between Na & Cl To write compound: 1 atom of Na needed for every 1 atom of Cl. So, compound formula = NaCl This is one molecule of NaCl
What happens when Na and Ca combine together? Write the ions for Na and Ca: Na +1 andCa +2 So, both ions are positive and so would repel each other Both atoms are trying to lose electrons.
What is the easiest way for potassium (K) to follow the Octet Rule? Lose 1 electron What is potassium’s oxidation number? +1 What is the easiest way for nitrogen (N) to follow the Octet Rule? Add 3 electrons What is nitrogen’s oxidation number? -3
Draw the valence of 3 K and 3 N atoms: K K K N N N What will happen when you combine these two elements? K loses 1 electron to N This K atom has a full valence But, this N atom does NOT have a full valence So, another K atom will lose an electron to N This K atom has a full valence How do you determine the compound formula? How many atoms are left with full valence These are the atoms in one molecule Always write POSITIVE ion first! Compound Formula = K 3 N