Atoms and Molecules Study Guide

Flashcards covering definitions, chemical formula reading, molecular modeling, simple and complex molecules, and extended structures from the MAT1 Seventh Grade Science Study Guide.

What is the definition of an atom?

The smallest part of a chemical element that can exist.

What is the definition of an element?

A type of matter in which each element has its own chemical symbol (e.g., Carbon C, hydrogen H, oxygen O).

What is a molecule?

Two or more atoms bonded together.

What is a compound molecule?

A molecule with atoms of two or more different elements bonded together (e.g., $H_2O$ contains hydrogen and oxygen).

What is a simple molecule?

A small group of bonded atoms with no continuing repeating pattern (e.g., water $H_2O$, ammonia $NH_3$, oxygen $O_2$).

What is an extended structure?

Atoms connected in a continuous, repeating pattern (e.g., sodium chloride $NaCl$ and diamond C).

How do an atom and a molecule differ?

An atom is one particle. A molecule is a group of two or more bonded atoms.

Can a molecule contain only one element?

Yes. For example, $O_2$ has two atoms, but both are oxygen. It is a molecule, but it is not a compound molecule.

What does an element symbol tell you in a chemical formula, and how is it formatted?

It tells which element is present. The first letter is capitalized, and a second letter is lowercase (e.g., Cu is one symbol; CO contains two symbols, C and O).

What does a subscript in a chemical formula indicate?

It tells how many atoms of that element are in one molecule. No subscript means one atom (e.g., $H_2O$ has 2 H atoms and 1 O atom).

What does a coefficient in a chemical formula indicate?

It tells how many separate molecules or single atoms are present. No coefficient means one (e.g., $3H_2O$ means 3 separate water molecules).

How do you calculate the total number of atoms of an element in a chemical formula?

Multiply the coefficient by that element's subscript. Then add the counts to find the total number of atoms.

In the chemical formula $2CO_2$, what do the big 2 and the little 2 mean?

The big 2 (coefficient) means there are two separate carbon dioxide molecules. The little 2 (subscript) means each molecule has two oxygen atoms.

For the formula $3H_2O$, what are the counts for different elements, total atoms, and molecules?

Different elements: $2$ (H and O); Atoms of each element: H = $6$, O = $3$; Total atoms: $9$; Molecules: $3$.

For the formula $4Ag$, how many molecules and total atoms are present?

Molecules: $0$ (it represents single atoms); Total atoms: $4$ Ag atoms.

In molecular diagrams such as the ones shown, what do the circles and lines represent?

Circles represent atoms and lines show connections (not bond types). Models are simplified.

Based on the provided diagram, what does the model for ammonia $NH_3$ show?

It shows 3 hydrogen atoms connected to 1 nitrogen atom, totaling 4 atoms and 2 different elements. It is a simple molecule and a compound molecule.

What are the 5 steps to make and check a molecular model?

1. Identify each element symbol in the formula. 2. Count the atoms of each element in one molecule. 3. Use labeled circles, blocks, or a ball and stick model to show the atoms and their connections. 4. If there is a coefficient, make that many separate copies of the molecule. 5. Check that the labels, atom counts, and number of separate groups match the formula.

What should a model of $3H_2O$ show?

Three separate water molecules. Each one has 2 H atoms and 1 O atom, for a total of 6 H atoms and 3 O atoms.

What is a complex molecule, and what are examples from the notes?

One larger molecule made of many atoms that may have repeated units. Examples include sugar $C_6H_{12}O_6$, proteins, DNA, and caffeine.

Why is the model of sodium chloride ($NaCl$) classified as an extended structure?

Its atoms form a repeating, connected pattern (lattice/crystal). The sketch shows part of a larger structure rather than a small, separate molecule.

How can you model an extended structure without drawing every single atom?

Draw a small section that shows the repeating pattern. Label the atoms and explain that the pattern continues.

How are monomers and polymers related, and what analogy is used in the notes?

A monomer is a small molecule that can link to others, while a polymer is a long chain of repeated monomers. A monomer is compared to one Lego block and a polymer to many connected blocks.