2.1 Properties of Atoms

Which choice correctly pairs the particles of an atom with their physical properties? A. proton-positively charged; neutron-negatively charged; electron-uncharged B. proton-uncharged; neutron-negatively charged; electron-positively charged C. proton-positively charged; neutron-uncharged; electron-negatively charged D. proton-negatively charged; neutron-uncharged; electron-positively charged

C. proton-positively charged; neutron-uncharged; electron-negatively charged

For an atom that is not an ion, which statement must be true? A) the number of electrons equals the number of neutrons B) the number of protons equals the number of neutrons C) the number of protons must be less than the number of electrons D) the number of electrons equals the number of protons

D) the number of electrons equals the number of protons

In the early 1900s, Ernest Rutherford produced a beam of very small positive charged particles and directed it at a thin piece of golf foil just a few atoms thick. Most of the particles passed through the foil without changing their path; very rarely, a particle was deflected. What conclusions can you draw from this experiment about the structure of an atom?

One conclusion is that atoms consist mainly of empty space, so most positively charged particles passing through the gold foil do not come close enough to any other positive charge to be deflected. Another conclusion is that the positively charged protons in the nucleus must be small and densely packed.

Element

a pure substance, such as oxygen, copper, gold, or sodium, that cannot be further broken down by the methods of chemistry

Orbital

a region in space where an electron is present most of the time

Ion

an electrically charged atom or molecule

Neutron

an electrically neutral particle in the atomic nucleus

Shell

an energy level

Isotopes

atoms of the same element that have different numbers of neutrons

Sometimes, atoms gain or lose particles. The loss of which particles would result in a change of overall electrical charge?

electrons and protons

What are atoms made up of? Describe each component.

An atom is made up of positively charged particles called protons, neutral particles called neutrons, and negatively charged particles called electrons. The dense central nucleus of an atom is made up of protons and neutrons. Electrons orbit around the nucleus, and the regions of space where they are most likely to be found are called orbitals.

Sometimes, atoms gain or lose particles. The loss of which particles would result in a change of atomic mass?

protons and neutrons

Periodic Table of the Elements

the arrangement of the chemical elements in tabular form, organized by their chemical properties

Atom

the basic unit of matter

Nucleus

the dense central part of an atom containing protons and neutrons

Atomic Mass

the mass of the atom determined by the number of protons and neutrons

What is the logic behind how the periodic table of the elements is organized?

The periodic table of elements is organized based on the increasing atomic number of each atom. The atomic number is the number of protons found in the nucleus of an atom. Hydrogen appears first in the periodic table because it has an atomic number of 1. The elements in a column share similar chemical properties, and each has the same number of electrons in its outermost orbital. Elements in a row have the same number of shells (energy levels), and thus the same number and types of orbitals.

Electron

a negatively charged particle that moves around the atomic nucleus

Proton

a positively charged particle in the atomic nucleus