Day L

It is possible for two elements to combine in different ways to form two or more different compounds, such as CO and CO2. When this occurs, the different masses of element B that combine with a fixed mass of element A can be expressed as a(n) of small numbers. This observation is summarized by the law of proportions.

Blank 1: ratio, proportion, or multiple Blank 2: whole Blank 3: multiple

isotopes

Isotopes have different numbers of neutrons. Isotopes of the same element have the same element symbols. Isotopes have similar chemical properties.

Each element in a given compound comprises a fixed fraction or percent by of the compound. This observation is summarized by the law of definite .

Mass Proportions

Which of the following correctly describe atomic structure? Select all that apply.

The number of protons equals the number of electrons in a neutral atom. The nucleus comprises a very small fraction of the total volume of the atom. The protons and neutrons together comprise most of the mass of the atom.

Which of the following options correctly describe Rutherford's experiment? Select all that apply.

This experiment used α particles to probe atomic structure. An α particle was known at this time to be positively charged. The pathway followed by the α particles was tracked using a zinc-sulfide screen.

Thomson's experiments with cathode rays determined that atoms contained even smaller particles called _____, which have a _____ charge.

electrons; negative

In a given chemical compound, the component _____ are present in _____ proportions by mass, regardless of the source of the compound.

elements; fixed

Each element has a unique number of , which is called the atomic number. For an electrically neutral atom, this number is also equal to the number of present.

protons, electrons

Which of the following options correctly describe the results of the experiments performed by Thomson and Millikan? Select all that apply.

Millikan's work allowed the charge of the electron to be calculated. Thomson studied the behavior of cathode rays. Millikan measured the electrical charge of oil droplets.

Which of the following statements correctly describe the observations that led to the development of the nuclear model of the atom? Select all that apply.

Rutherford determined that the main mass of the atom is concentrated in a central region. The discovery of cathode rays led to an understanding that the atom contains smaller particles. Thomson measured the mass/charge ratio for an electron.

Isotopes are atoms of the same element that have the same _____ number but a different _____ number. This is because isotopes have the same number of protons but a different number of _____.

atomic; mass; neutrons

Rutherford's famous experiment involved bombarding a piece of foil with particles, which were known to be heavy and positively charged. The pathway of these particles was tracked by allowing them to strike a zinc-sulfide screen after interacting with the foil.

gold, alpha

the atomic mass unit

is often abbreviated as amu is based on the mass of an atom of C612

During a chemical reaction, the total _____ of the substances present does not change. The number of substances may change, but the total amount of matter present _____.

mass; remains unchanged

Water (H2O) contains 8.0 g O for every 1.0 g of H and hydrogen peroxide (H2O2) contains 16.0 g O for every 1.0 g of H. Therefore, the ratio of the masses of oxygen that combine with a fixed amount of hydrogen in the two compounds is a small whole number ratio of 2:1. This is an example of the law of _____.

multiple proportions

An atom is composed of a very dense central containing , which are positively charged, and neutrons, which have electrical charge.

protons; zero

True or false: After the completion of a chemical reaction, the number of substances may have changed but the amount of matter remains constant.

t

The law of multiple proportions states that if two elements A and B combine to form two compounds, the different masses of B that combine with a fixed mass of A are ______.

the ratio of small whole numbers

Which of the following statements correctly describe the atomic number of an element? Select all that apply.

- The atomic number is equal to the number of protons in the nucleus - each element has its own unique atomic number