How do you know whether a compound is ionic or covalent and how can you find the conductivity rate for both heat and electricity?

As a general rule metals bind to non-metals ionically, and non-metals to non-metals bind covalently. For example NH3 is covalent, vs NaCl is ionic. Conductivity rates for electricity are in general dependent on the number of delocalised electrons in a compound. For example, graphite is conductive to electricity as it has delocalised electrons (each carbon is bound to 2 other carbons, leaving one free electron to delocalised). Diamond is not conductive to electricity, as each carbon is bound covalently to 3 others, so has no free electrons. Mainly Metals are conductive to heat, as each metal atom isn't bound to another directly - they're positive ions in a sea of delocalised electrons. The electrons and positive ions therefore can transmit the heat energy to each other without covalent bonds getting in the way.