About 25 of the 92 natural elements are known to be essential to life. Which four of these 25 elements make up approximately 96% of living matter?
Carbon, hydrogen, nitrogen, oxygen
Trace elements are those required by an organism in only minute quantities. Which of the following is a trace element that is required by humans and other vertebrates?
Iodine
Which of the following statements is false?
Protons and electrons are electrically charged particles. Protons have one unit of negative charge, and electrons have one unit of positive charge.
Each element is unique and different from other elements because of the number of protons n the nuclei of its atoms. Which of the following indicates the number of protons in an atoms nucleus?
atomic number
One difference between carbon-12 (12, 6 C) and carbon-14 (14, 6 C) is that carbon-14 has
two more neutrons than carbon-12
3His a radioactive isotope of hydrogen. One difference between hydrogen-1 (1, 1 H) and hydrogen-3 (3, 1 H) is that hydrogen-3 has
two more neutrons than hydrogen-1.
The atomic number of carbon is 6. Carbon-14 is heavier than carbon-12 because the atomic nucleus of carbon-14 contains _____ neutrons.
8
Two isotopes of the same element will have different numbers of
neutrons
Electrons exist only at fixed levels of potential energy. However, if an atom absorbs sufficient energy, a possible result is that
an electron may move to an electron shell farther out from the nucleus