BackAtoms and Elements: Structure, Properties, and Periodic Trends
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Atoms and Elements
Introduction to Atoms
All matter, whether simple or complex, is composed of atoms—the fundamental building blocks of chemistry. The term atom comes from the Greek word meaning “unable to cut,” signifying its indivisible nature in chemical processes. Understanding atomic structure is essential for grasping the properties and behavior of elements and compounds.
Atoms are the smallest units of matter that retain the identity of an element.
Each atom consists of a nucleus (containing protons and neutrons) and an electron cloud.
Atoms combine to form molecules and compounds, which make up all substances.
What is an Atom Made Of?
An atom is composed of three primary subatomic particles: protons, neutrons, and electrons. Their arrangement and properties determine the identity and behavior of each element.
Protons and neutrons are located in the nucleus at the center of the atom.
Electrons move rapidly around the nucleus in the electron cloud.
Most of the atom's volume is empty space, with the nucleus occupying a tiny central region.
Scale Example: If a hydrogen atom were the size of a stadium, its proton would be the size of a pea, illustrating the vast empty space within atoms.
Subatomic Particles
The three subatomic particles have distinct properties:
Proton (p+): Positive charge (+1), located in the nucleus.
Neutron (n0): No charge (neutral), located in the nucleus.
Electron (e-): Negative charge (-1), found in the electron cloud.
Atoms are electrically neutral when the number of protons equals the number of electrons.
Mass of atom: Determined by the sum of protons and neutrons.
Symbols of Elements
Elements are represented by unique symbols and numbers that convey their atomic structure.
Element Symbol: One or two letters (e.g., C for carbon).
Atomic Number (Z): Number of protons in the nucleus; defines the element.
Mass Number (A): Total number of protons and neutrons.
Example: represents carbon with 6 protons and 6 neutrons.
Isotopes
Isotopes are atoms of the same element with different numbers of neutrons, resulting in different mass numbers.
All isotopes of an element have the same number of protons and electrons.
Isotopes differ in the number of neutrons.
Isotope | Protons (p+) | Neutrons (n0) | Electrons (e-) |
|---|---|---|---|
6 | 5 | 6 | |
6 | 6 | 6 | |
6 | 7 | 6 | |
6 | 8 | 6 |
Example: Carbon-12 and Carbon-14 are both carbon atoms but have different numbers of neutrons.
Atomic Structure: Nucleus and Electron Cloud
The atom consists of a dense nucleus and a surrounding electron cloud:
Nucleus: Contains protons and neutrons; responsible for most of the atom’s mass.
Electron Cloud: Contains electrons; responsible for most of the atom’s volume and is mostly empty space.
Key Definitions
Atomic Number (Z): Number of protons in the nucleus.
Mass Number (A): Number of protons plus neutrons.
Isotope: Atoms of the same element with different numbers of neutrons.
Electron Cloud: Region around the nucleus where electrons are likely to be found.
Summary Table: Subatomic Particles
Particle | Symbol | Charge | Location |
|---|---|---|---|
Proton | p+ | +1 | Nucleus |
Neutron | n0 | 0 | Nucleus |
Electron | e- | -1 | Electron cloud |
Example Application
Given (Carbon-13):
Protons: 6
Neutrons: 7
Electrons: 6
This information is essential for identifying isotopes and understanding atomic mass.
Additional info: These notes cover the foundational concepts of atomic structure, including subatomic particles, isotopes, and atomic symbols, which are central to General Chemistry.
