Counting Atoms in Compounds and Molecules

The video tutorial covers the topic of counting atoms in chemical compounds. It introduces four key rules: identifying elements by capital letters, understanding subscripts, using coefficients, and applying parentheses in chemical formulas. The tutorial includes practice examples and explains the law of conservation of mass, emphasizing the importance of balancing chemical equations.

What does the capital letter in a chemical element symbol indicate?

• The number of atoms in the compound

• The atomic number of the element

• The molecular weight of the element

• The start of a new element in the formula

If a chemical element symbol in a formula does not have a subscript, how many of that element are present?

• Two

• It varies depending on the element

• One

• Zero

What does a subscript in a chemical formula indicate?

• The number of atoms of the element it follows

• The charge of the molecule

• The isotopes of the element

• The number of molecules

What does the absence of a subscript after an element symbol typically mean?

• There are no atoms of that element present

• There are two atoms of that element present

• The element is inert in the reaction

• There is one atom of that element present

How does a coefficient outside a chemical formula affect the atoms inside the formula?

• It decreases the number of atoms

• It only affects the first element in the formula

• It multiplies the number of each atom by the coefficient

• It has no effect

How do you determine the total number of atoms in a compound with coefficients?

• Multiply the coefficient by the number of atoms indicated by subscripts

• Divide the coefficient by the number of atoms

• Add the coefficients

• Coefficients do not affect atom count

What is the effect of a subscript outside parentheses in a chemical formula?

• It multiplies the number of atoms inside the parentheses

• It reduces the number of atoms to one

• It indicates a new molecule

• It applies only to the element directly before it

What role do parentheses play in a chemical formula?

• They group elements that are treated as a single unit

• They separate molecules from each other

• They indicate optional elements

• They are used for aesthetic purposes only

According to the law of conservation of mass, what must be true about a chemical reaction?

• Energy must be conserved, not mass

• The products must be gaseous

• The number of each type of atom must be the same in reactants and products

• The reactants must weigh more than the products

Tags

NGSS.HS-PS1-7

In a balanced chemical equation, what must be true about the atoms of each element?

• They must be catalyzed

• They must all be gases

• They must transform into new elements

• They must be in equal proportions on both sides

Tags

NGSS.HS-PS1-7