The answer is to do with electronegativity difference. Metals generally have low values and non metals higher values. When an element with a low value combines with an element with a high value, usually the element with the low value LOSES electrons to form a positive ion while the other element gains the electron(s) and forms a negative ion. So an ionic compounds is formed. Compoiunds of this type usually contain a metal elements joined to non-metal element - so compounds 2 and 3 in your list are ionic.
When the compound is made from only non-metal elements, electrons are not lost or gained but shared as these elements tend not to lose electrons or gain them. Instead they share electrons to make covalent bonds. If the result are small structures they will be molecular eg 1 and 4 in your list.
C3H8, Cl2O
no
All elements and all compounds do not exist as molecules. As examples, noble gases exist as individulal atoms and ionic compounds form lattices.
Organic compounds exist as discrete molecules with much weaker inter molecular forces than those seen in ionic compounds?
yes it can
Covalent compounds usually exist as small, seperate molecules. Although there are exceptions such as diamond and graphite.
no
All elements and all compounds do not exist as molecules. As examples, noble gases exist as individulal atoms and ionic compounds form lattices.
Organic compounds exist as discrete molecules with much weaker inter molecular forces than those seen in ionic compounds?
yes it can
Covalent compounds usually exist as small, seperate molecules. Although there are exceptions such as diamond and graphite.
Ionic compounds conduct electricity while molecular compounds do not
I'm on dat good kush and alcohol.
Many ionic compounds exist as crystals but covalent compounds as molecules (there are exceptions as diamond though). Ionic compounds would be good electrical conductors unlike molecular compounds.
Aluminum is an element, composed of molecules, is on the periodic chart, does exist by itself AND can be combined to form compounds.
All elements and compounds are present in molecular state. They cannot be found as individual atoms. Atoms cannot exist in free state.
Under normal conditions of temperature and pressure, neon forms no elemental molecules. It can possibly form compounds with some other, extremely electronegative, elements. These compounds, if they exist, would have formulas.
No metals form molecules; they only exist as ionic compounds or metallic elements or alloys.