TEAS 7 · Science · 7 min read
Atoms, the Periodic Table and Chemical Bonds
- Differentiate between the fundamental properties and states of matter, and describe how subatomic particles define atomic identity, isotopes, and ions.
- Explain how elements are organized on the periodic table and identify key trends in atomic radius, electronegativity, and ionization energy.
- Compare ionic, covalent, and hydrogen bonds, and explain how valence electrons and electronegativity govern chemical interactions.
Principles of Matter and States of Aggregation
Matter is anything that has mass and takes up space; the physical universe also includes energy, such as light, which is not matter. Mass is the measure of the amount of matter contained within an object, while volume is the measure of the amount of space that an object occupies. When evaluating how tightly packed that matter is, scientists examine density, which is calculated by dividing mass by volume. A dense object contains a large amount of mass within a relatively small volume.
Matter possesses both physical and chemical properties that help describe its nature and behavior. Physical properties can be observed or measured without altering the chemical identity of a substance. In contrast, chemical properties describe a substance's ability to undergo chemical reactions that produce entirely new substances. Observing or measuring a physical property does not change a substance’s chemical identity, although it may change its physical form; observing a chemical property involves a reaction that produces different substances.
Matter primarily exists in three primary states: solid, liquid, and gas. These states differ based on their shape and volume characteristics. Solids have a definite shape and a definite volume, holding their form regardless of the surrounding environment. Liquids possess a definite volume but lack a fixed shape, taking the shape of their container while maintaining a constant amount of space. Gases have neither a definite shape nor a definite volume, expanding freely to fill whatever container they occupy.
| State of Matter | Definite Shape | Definite Volume | Container Behavior |
|---|---|---|---|
| Solid | Yes | Yes | Maintains its own shape and volume independently |
| Liquid | No | Yes | Takes the shape of its container while keeping a fixed volume |
| Gas | No | No | Expands to match both the shape and volume of its container |
Common mistakes
- Confusing mass number with atomic number: Mass number is the sum of protons and neutrons in the nucleus, whereas atomic number counts only protons and identifies the element.
- Reversing the charges of ions: Assuming that gaining electrons makes an ion positive. Because electrons carry a negative charge, gaining electrons forms a negatively charged anion, while losing electrons forms a positively charged cation.
- Misidentifying hydrogen's classification: Assuming hydrogen is an alkali metal because it sits in Group 1; hydrogen is located in Group 1, but it is not an alkali metal.
- Thinking all covalent bonds share electrons equally: Covalent bonds only share electrons equally (or nearly equally) when bonded atoms have identical or very similar electronegativities (nonpolar); unequal sharing occurs when electronegativities differ (polar), giving the more electronegative atom a partial negative charge.
Key points
- Matter has mass and volume, with density calculated by dividing mass by volume; it exists primarily as solids (definite shape and volume), liquids (definite volume, container shape), or gases (neither definite shape nor volume).
- Atoms consist of a dense nucleus containing positive protons and neutral neutrons, surrounded by an electron cloud of negative electrons in orbitals; protons and neutrons have significantly greater mass than electrons.
- The atomic number equals the number of protons, the mass number equals protons plus neutrons, isotopes differ in neutron count, and ions form when atoms lose electrons (cations) or gain electrons (anions).
- The periodic table organizes elements by increasing atomic number into horizontal periods and vertical groups; main-group elements in a group share valence electron counts (helium has two, other group 18 elements have eight) and chemical properties.
- Across a period, atomic radius decreases while electronegativity and ionization energy increase; down a group, atomic radius increases while electronegativity and ionization energy decrease.
- Ionic bonds form when a metal transfers electrons to a nonmetal and oppositely charged ions attract; covalent bonds form when atoms share valence electrons, either equally (nonpolar) or unequally (polar).
- Hydrogen bonds are attractions between a hydrogen atom covalently bonded to nitrogen, oxygen, or fluorine and a nearby atom with an available lone pair of electrons; hydrogen bonding contributes to water's high specific heat and surface tension.
Practice this section
Explained TEAS Science questions, no account needed. TEAS Science practice test
The full lesson continues with 4 more sections with exam tips, audio in English and Spanish, 5 Check yourself questions and 20 flashcards.
- 1 month
$53.99$26.99 - 3 months
$158.99$79.49 - Lifetime
$323.99$161.99
One payment, no subscription.
See TEAS plansAlready a member? Log in
Sample lesson: The Heart and Blood Flow25 practice questions on this exam
Each TEAS practice test has 25 original questions with the answers explained. No account needed.
Open the TEAS practice testsOriginal lesson written for TEAS 7 practice · updated October 15, 2026. Exam names are trademarks of their owners; tests.global is not affiliated with them.