2.4.1 Describing Chemical Formulas Flashcards
Describing Chemical Formulas
- Atoms, molecules, ions, ionic compounds, and covalent solids are all different units of matter.
- Chemical formulas are a “chemical shorthand” to quickly and accurately identify compounds.
- Chemical formulas can be represented graphically in many different ways.
atoms, molecules, ions
- Atoms are the smallest units of an element.
- Molecules are well-defined groups of atoms that are
chemically bonded together. - Ions are charged particles that are obtained from atoms by adding or removing electrons. These are also polyatomic ions.
- Ionic compounds and covalent solids are three-dimensional repeating structures. Ionic compounds are composed of positive ions (cations) and negative ions (anions) in a set ratio. Covalent solids are composed of covalently bonded atoms in a fixed ratio
chemical formulas
- Chemical formulas are a “chemical shorthand” to quickly and accurately identify compounds.
- Molecular formulas represent the actual number of atoms of each element in a molecule. For example, the molecular formula for benzene is C6H6.
- Empirical formulas represent the simplest integer ratio of the elements in a compound. For example, the empirical formula for benzene is CH. The empirical formula does not always uniquely identify a molecule—CH could be benzene (C6H6), but it could also be ethyne (C2H2).
- Chemical formulas can be represented graphically in many different ways.
- A line drawing allows chemists to see how the individual atoms connect together.
- A shorthand is used by organic chemists to quickly write common molecules.
- A ball and stick representation closely resembles the actual geometry of a molecule.
- A space filling representation shows what a molecule would look like magnified.
NH4+ is an example of
a cation.
Which of the following statements is false?
Butane and 2-methylpropane form lattices.
- The structural formulas above show that each substance has a molecular structure, not a lattice structure. Lattices are potentially infinite arrays of well-defined ratios, but undefined numbers, of types of ions or atoms forming either an ionic salt or a covalent lattice. There is no clear way to identify a molecule of these types of substances.
For sodium chloride, an ionic compound, which of the following can you NOT do?
Write a molecular formula.
- Sodium chloride is an ionic salt, which forms a lattice. There is no defined molecular boundary. The ratio of one element to the other can be determined, but not the exact number of each element. Therefore, a molecular formula cannot be written.
A molecule of caffeine consists of 8 carbon atoms, 10 hydrogen atoms, 4 nitrogen atoms, and 2 oxygen atoms. Which of the following represents the empirical formula for caffeine?
C4H5N2O
Sulfate (SO42− ) is
a polyatomic anion.
_____________________ are discrete packages of atoms connected together in well-defined numbers and ratios with no overall charge.
Molecules
Which of the following is a molecule?
CO2
C2H2 is a chemical formula for acetylene. Which type of chemical formula is it?
A molecular formula
Which of the following statements is false?
A molecular formula uniquely describes a molecule
The following is a ball-and-stick drawing of the compound cis 1,2-dichloroethene.
What is the empirical formula for 1,2-dichloroethene?
CHCl