Chemistry First Semester Final Practice Test - Period 4

Front

What is the half-life of a radioactive isotope?

Back

The half-life is the time required for half of the radioactive atoms in a sample to decay. For example, if the half-life is 5.00 × 10³ years, it means that after this time, half of the original amount of the isotope will remain.

Front

Convert 5.00 × 10³ years to days using scientific notation.

Back

1.83 × 10⁶ days (calculated as 5.00 × 10³ years × 365 days/year).

Front

Which subatomic particle has no charge?

Back

Neutron.

Front

What are representative elements in the periodic table?

Back

The elements in groups 1, 2, and 13-18 are known as representative elements, which include metals, nonmetals, and metalloids.

Front

What is a chemical change?

Back

A chemical change involves a transformation that alters the chemical composition of a substance, such as wood burning.

Front

What is the charge of an ion with 18 electrons and 20 protons?

Back

+2 (The charge is calculated as protons - electrons = 20 - 18 = +2).

Front

Define ion.

Back

An ion is an atom or molecule that has a net electrical charge due to the loss or gain of one or more electrons.

Front

What is the difference between a physical change and a chemical change?

Back

A physical change alters the form or appearance of a substance without changing its chemical composition, while a chemical change results in the formation of new substances.

Front

What are alkali metals?

Back

Alkali metals are the elements in group 1 of the periodic table, known for being highly reactive and having one electron in their outermost shell.

Front

What is the significance of significant figures in scientific calculations?

Back

Significant figures indicate the precision of a measurement and help convey the certainty of the data.