Chapter 4

Early Atom Concepts

Democritus's Atomic Philosophy

Democritus stated that atoms were unchangeable and indestructible

He was the first to suggest atoms existed.

Many people disagreed with his ideas because they lacked experimental data.

Dalton's Atomic Theory

Dalton's theory took place more than 2000 years after Democritus.

Dalton used Democritus's ideas on atoms into a scientific theory by using experimental methods.

Dalton studied the ratios of elements that combined in chemical reactions, and used his results to formulate hypotheses.

He was able to conclude 4 results.

Elements are composed of tiny indivisible particles called atoms.

Atoms of the same element are identical and all atoms from one element are different from those in another element.

Atoms from different elements can combine together in whole number ratios to form compounds.

A chemical reaction doesn't happen when atoms are separated, conjoined, or rejoined together.

Three Subatomic Particles

Electrons

Protons

Neutrons

J.J. Thompson discovered them in 1897.

Negatively charged subatomic particles.

Eugen Goldstein discovered them in 1886.

Positively charged subatomic particles.

Has a mass 1840 times greater than an electron

James Chadwick discovered it in 1932.

No charge, Neutral subatomic particles.

Has a mass nearly equal to a proton.

Structure Of An Atom

Nucleus is the core of an atom composed of protons and neutrons

Electron Cloud is the area surrounding an atom where an electron will most likely be found.

What Makes One Element Different Than Another

Atomic Number is the number of protons in the elements' nucleus.

Mass Number is the number of protons and neutrons all together in an atom.

Isotopes are atoms with the same number of protons but different number of atoms

Atomic Mass is the average mass of the atoms naturally in a specific element, and it reflects the mass and the relative abundance of the isotopes.

Atomic Mass Unit is defined as 1/12th of the mass of a carbon-12 atom.

To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

Periodic Table arranges elements by groups that are based on sets of repeating properties.

Period is the horizontal row.

Group is the vertical column.