Ch 1 - Atoms

What is the main characteristic difference between a solid and a liquid in terms of particle arrangement?

In a solid, particles are closely packed in an ordered arrangement, while in a liquid, they are close together but in a random arrangement.

How can mixtures be separated, and what are the two main types of mixtures?

Mixtures can be separated by physical processes. The two main types are homogeneous mixtures (uniform distribution, no visible boundaries) and heterogeneous mixtures (non-uniform distribution, distinct regions).

Define an element and explain why it cannot be broken down using chemical reactions.

An element is a pure substance consisting of only one type of atom. It cannot be broken down by chemical reactions because it is composed of atoms that are indivisible by chemical means.

Describe the structure of an atom, including the location and charge of protons, neutrons, and electrons.

An atom consists of a nucleus containing protons (charge of 1+, mass number 1) and neutrons (neutral charge, mass number 1). Electrons are located outside the nucleus with a charge of 1- and negligible mass.

Explain the difference between mass number and atomic mass.

Mass number is the total number of protons and neutrons in an atom's nucleus, whereas atomic mass is the weighted average of an element's isotopes, usually not a whole number.

What does Avogadro's number represent and why is it significant in chemistry?

Avogadro's number (6.0221 x 10^23) represents the number of atoms, ions, or molecules in one mole of a substance. It is significant because it allows chemists to count particles in macroscopic amounts of material.

Define a cation and an anion.

A cation is a positively charged ion that forms when an atom loses electrons. An anion is a negatively charged ion that forms when an atom gains electrons.

How do you calculate the molar mass of a compound?

The molar mass of a compound is calculated by summing the atomic masses of all the atoms present in the molecular formula of the compound.

In isotopic representation, what do the symbols Z, A, and X stand for?

In isotopic representation, Z is the atomic number (number of protons), A is the mass number (sum of protons and neutrons), and X is the chemical symbol of the element.

What is a molecule, and how does it differ from a compound?

A molecule is a group of atoms bonded together. It can be a compound if it consists of different elements, but molecules can also consist of a single element (e.g., O2).

Why is atomic mass not a whole number?

Atomic mass is not a whole number because it is the weighted average of all the isotopes of an element, based on their abundance in nature.

How are the properties of a gas different from those of a liquid in terms of definite shape and volume?

A gas has neither a definite shape nor a definite volume and expands to fill its container, whereas a liquid has a definite volume but no definite shape, conforming to the shape of its container.

What is the significance of the atomic number (Z) in the periodic table?

The atomic number (Z) is the number of protons in an atom's nucleus and determines the identity and position of an element in the periodic table.

Explain the mole concept and its importance in chemical calculations.

The mole concept relates the microscopic scale (atoms and molecules) to the macroscopic scale. It allows chemists to convert between number of particles and mass using Avogadro's number, making it crucial for chemical calculations.

What is the relationship between an atom's mass number and its isotopes?

The mass number of an atom (sum of protons and neutrons) can vary in isotopes of an element, as isotopes have the same number of protons but different numbers of neutrons.