CHEM1202 1.3- Density and Chemical Formulae

Lec 3

What is the definition of density?

Density is mass per unit volume, typically expressed as g/cm³.

How do you calculate the density of a substance?

Density is calculated by dividing the mass of the sample by the volume it occupies.

What is the density of water?

1.00 g/cm³.

What does atomic number (Z) represent?

The atomic number represents the number of protons in the nucleus of an atom, defining the element.

What is the significance of a chemical formula?

A chemical formula indicates the atoms present in a compound and the relative number of each type of atom.

Why are compounds considered neutral?

Compounds are neutral because they contain equal amounts of positive and negative charges.

What is the formula for ammonia?

NH3.

How do you determine the chemical formula for a compound?

The formula is determined by the valency of the elements and ensuring a neutral charge overall.

What is a polyatomic ion?

A polyatomic ion is a group of atoms that behaves as a single unit with a charge.

What does the valency table help predict?

The valency table helps predict the charge on the most common ion for various elements.

What is the density of ethylene glycol (C2H6O2)?

1.1 g/cm³.

How can we predict the combination of aluminum with chlorine?

By using the valency table: Aluminum has a +3 charge, and each Chlorine has a -1 charge, so three Chlorine atoms are needed (AlCl3).