Atomic Structure and Isotopes Practice Quiz (16 questions)

Explanation

An element is a pure substance that cannot be broken down into simpler substances. A mixture combines matter, a compound can be broken down chemically, and an atom is a particle rather than the substance classification.

Explanation

An element contains only one type of atom, and atoms are the particles that make up an element. A mixture contains different kinds of matter, while a single atom is one particle and a compound is not defined by having one atom type.

Explanation

Metals are generally shiny, conduct heat and electricity well, and can be bent or hammered into sheets. Metalloids conduct less well than metals, while dullness and brittleness are typical of solid nonmetals.

Explanation

Metalloids are solid at room temperature, have both metallic and nonmetallic characteristics, are less brittle than nonmetals, and conduct electricity less well than metals. Metals conduct better, while solid nonmetals tend to be brittle.

Explanation

By the mid-1800s, most scientists agreed that each element was made up of a unique type of atom. The early consensus did not describe internal charged particles or shared atom types across elements.

Explanation

The mid-1800s view treated atoms as tiny, indivisible balls that differed only in mass. Descriptions involving internal particles belong to later models, and the early view did not claim that atoms were identical across elements.

Explanation

Because atoms are too small to observe directly, models help scientists visualize their structure. Direct inspection confuses representation with observation, exact-distance measurement overstates what a model necessarily provides, and true-scale reproduction overlooks the difficulty of constructing scale models.

Explanation

When relative sizes and distances are not the focus, a not-to-scale model can show particle numbers, charges, and locations. A scale model for distances addresses a different need, relative sizes are not essential here, and omitting numbers and charges misses the stated purpose.

Explanation

The atomic number equals the number of protons in the nucleus and identifies a specific element. Mass number counts protons plus neutrons, electron number concerns particles outside the nucleus, and neutron number does not define the element.

Explanation

Mass number is the total of protons and neutrons, so $9 + 10 = 19$. The value 9 is the atomic number, adding an unspecified electron count uses the wrong particles, and an isotope-weighted average describes average atomic mass for a sample.

Explanation

A neutral atom has equal numbers of protons and electrons, so 12 protons means 12 electrons. Matching neutrons to protons is a different relationship, while 11 or 13 electrons would make the atom electrically charged.

Explanation

Isotopes are atoms of the same element with the same numbers of protons and electrons but different numbers of neutrons. Ions differ in electron count, different elements have different proton counts, and identical isotopes have matching neutron counts.

Explanation

Multiply each isotope’s exact mass by its decimal abundance and sum: $10(0.25)+11(0.75)=2.5+8.25=10.75\text{ u}$. An unweighted mean ignores abundance, adding abundances is not the required operation, and the stated weighted products do not equal 11 u.

Explanation

The periodic-table atomic mass averages the element’s isotopes while accounting for their relative abundances. A mass number is the proton-and-neutron total in one atom; the proton count is the atomic number, and the neutron count is not the listed average.

Explanation

Estimate the most common isotope’s mass number by rounding the average atomic mass to the nearest whole number; 24.3 rounds to 24. Choosing 25 rounds in the wrong direction, 24.3 is not a whole-number mass number, and 20 rounds to the nearest ten instead.

Explanation

A flame test uses properties of elements to help identify an unknown substance. Measuring quantity, determining proton count, and measuring temperature are different goals, not the stated purpose of the test.