Question

choose the best answers.
2.11) ______ a pure substance that is made of only one kind of atom is called a(n)
a. element b. compound c. molecule
2.12) ______ elements differ from each other because they each have a different nu
of ____.
a. electrons b. protons c. neutrons
2.13) ____ of __ elements are found naturally on the earth.
a. 95; 115 b. 90; 110 c. 98; 118
2.14) ____ new elements __ being discovered by scientists.
a. are b. are not
molecules and compounds

Explanation:

• 2.11: An element is a pure substance made of only one kind of atom. A compound is made of two or more different kinds of atoms chemically combined. A molecule is a group of atoms bonded together.
• 2.12: Elements differ from each other because they each have a different number of protons. The number of protons (atomic number) defines an element. Electrons can be lost or gained (ions) and neutrons can vary (isotopes) without changing the element.
• 2.13: 98 of 118 elements are found naturally on the earth. The remaining are synthetic (man - made).
• 2.14: New elements are being discovered by scientists. Scientists use particle accelerators and other techniques to create and detect new elements.

Answer:

2.11) A. element
2.12) B. protons
2.13) C. 98; 118
2.14) A. are