Periodic Table

About how many known elements are in the periodic table?

• 10

• 50

• 100

• 200

Answer explanation

There are about 118 known elements in the periodic table. As scientists continue to experiment with particle accelerators and cyclotrons, they will be able to make more elements. Many of the manmade elements in the table only exist for a few milliseconds before they break apart.

Elements in the periodic table are arranged by...

• Atomic mass

• Atomic number

• Number of neutrons

• Chemical reactivity

Answer explanation

The elements in the periodic table are organized by atomic number. Hydrogen (H) and helium (He) make up the top row of the periodic table at numbers one and two, respectively. The atomic number represents the number of protons and electrons in a neutral atom. You may also hear the term ‘proton number’ used instead of ‘atomic number’.

Which of these things are NOT listed in the periodic table?

• Element name or symbol

• Atomic mass

• Atomic orbital radius

• Atomic number

Answer explanation

You will not find information about the atomic radius of an atom in the periodic table. The square for each element will have the atomic number, atomic weight, name, and symbol for each element.

Which scientist came up with the concept of a periodic table?

• Jason Priestly

• Henry Moseley

• Antoine Lavoisier

• Dmitri Mendeleev

Answer explanation

Dmitri Mendeleev gets the credit for designing the modern periodic table. Jason Priestly is an actor. Joseph Priestly and Antoine Lavoisier were both chemists. Albert Einstein developed theories about atomic particles.

The rows of the periodic table are called periods.

• True

• False

Answer explanation

The rows of the periodic table are called periods. The columns of the periodic table are called groups. Periods are loosely organized by the number of atomic orbitals found in each element. For example, hydrogen (H) in the first row has only one orbital. Lithium (Li) in the second row has electrons in two orbitals. Francium (Fr), in row seven, has electrons in seven orbitals.

Which of these is NOT a family of elements?

• Halogens

• Alkali Metals

• Transition Metals

• All of these are families

Answer explanation

All of these choices are different types and families of elements. Inert gases can be found on the far right of the periodic table in group VIIIA. Halogens are just to the left in VIIA. Metals make up the center and left side of the table in a variety of groups.

The atomic number of an element tells you the number of _____ in an atom.

• Protons

• Neutrons

• Electrons

• None of the above

Answer explanation

The atomic number of an element tells you the number of electrons and protons in a neutral atom. Ions are atoms of an element with different numbers of electrons. Isotopes are forms of an element with different numbers of neutrons.

The columns of the periodic table are called groups.

• True

• False

Answer explanation

The columns of the periodic table are called groups. In some cases, those columns represent families of elements. For example, the first column (Group IA) is the family of alkali metals with lithium (Li), sodium (Na), and potassium (K). The rows of the periodic table are called periods. At the end of every period is a noble gas in group VIIIA.

You will find metals on the far right column of the periodic table.

• True

• False

Answer explanation

Noble gases are found on the far right of the periodic table in group VIIIA. Halogens are in the second group from the right. Metals of all types are found around the left side of the periodic table. There may be earth, transition, or alkaline earth metals across the table.

Although the order of elements is based on atomic number, vertical families share similar chemical properties.

• True

• False

Answer explanation

Elements in the same groups, such as the halogens or noble gases, often share similar chemical properties. These properties might include relative atomic radius, electronegativity, or ionization energy. All of the noble gases are very nonreactive, while all of the halogens are very reactive.