7.6B, 8.6B & 8.6E Quiz

What do scientists use to identify the elements present in a molecule?

• chemical symbol

• subscript

• elements in Group 18

• chemical formula

Answer explanation

Scientists use a chemical formula to identify the elements in a molecule, as it shows the types and quantities of atoms present. Other options like chemical symbols and subscripts are components of the formula, but not standalone identifiers.

Tags

NGSS.MS-PS1-1

When do we use parentheses in a chemical formula?

• any time there is a subscript

• only when we have a coefficient

• when there is a special subgroup of atoms

• whenever there is an invisible “1”

Answer explanation

Parentheses in a chemical formula are used to indicate a special subgroup of atoms, such as polyatomic ions. This helps clarify the structure and composition of the compound, especially when subscripts apply to the entire group.

What does a subscript tell us?

• how many atoms of each element are in a molecule

• the charge of the ion

• the amount of molecules in a reaction

• the atomic number of the element

Answer explanation

A subscript in a chemical formula indicates the number of atoms of each element present in a molecule. For example, in H2O, the '2' indicates there are two hydrogen atoms for every one oxygen atom.

Tags

NGSS.MS-PS1-1

What are chemical formulas made up of?

• electrons and coefficients

• chemical symbols and subscripts

• molecules and elements

• atoms and electrons

Answer explanation

Chemical formulas are composed of chemical symbols, which represent elements, and subscripts, which indicate the number of atoms of each element in a molecule. Thus, the correct answer is 'chemical symbols and subscripts'.

Tags

NGSS.MS-PS1-1

If there is no number after a chemical symbol, how many atoms of that element are there?

• 0

• 1

• 2

• We do not know how many.

Answer explanation

If there is no number after a chemical symbol, it indicates that there is 1 atom of that element present. Therefore, the correct answer is 1.

Tags

NGSS.MS-PS1-1

When are parentheses needed in a chemical formula?

• never

• always

• to group certain atoms together

• when there is an invisible “1”

Answer explanation

Parentheses are needed in a chemical formula to group certain atoms together, especially when indicating multiple identical groups or when a subscript applies to a group of atoms rather than a single atom.

What inspired Dmitri Mendeleev to create the periodic table?

• He wanted to win a scientific competition.

• He noticed patterns and connections among elements.

• He was trying to create a new type of element.

• He was following the instructions of his professor.

Answer explanation

Dmitri Mendeleev was inspired to create the periodic table because he noticed patterns and connections among elements, which allowed him to organize them based on their properties and atomic weights.

Elements in the same group have what in common?

• chemical properties

• physical properties

• atomic mass

• atomic number

Answer explanation

Elements in the same group of the periodic table share similar chemical properties due to their similar valence electron configurations, which influence their reactivity and bonding behavior.

What are the horizontal rows in the periodic table called?

• groups

• columns

• periods

• families

Answer explanation

The horizontal rows in the periodic table are called periods. Each period represents a different energy level of electrons in the atoms, distinguishing them from groups or families, which are the vertical columns.

Which reaction involves elements from Group 2 and Group 16?

• H₂​ +Cl_2​ → 2 HCl

• Na+Cl₂ ​→ 2 NaCl

• 4 Fe+3O_2​ → 2 Fe_2​O_3​

• 2 Ca+O₂​ → 2 CaO

Answer explanation

The reaction 2 Ca + O2 → 2 CaO involves calcium (Ca) from Group 2 and oxygen (O) from Group 16, making it the correct choice. The other reactions do not involve elements from these specific groups.