CH 1000 MOD 1 REVIEW HW

CH1000 Fundament als of Chemistry Module 1 – Chapter 5

Dalton’s Model of the Atom (Early 1800s)

• Elements are composed of small, indivisible particles called atoms. • Atoms of the same element are identical in mass and size. • Atoms of different elements differ in their mass and size. • Compounds are formed by combining two or more atoms of different

elements. • Atoms combine to form compounds in simple whole number ratios. • Atoms of two elements may combine in different ratios, leading to

formation of different compounds.

Revisions to Dalton’s Theory

• Elements can be decomposed under certain conditions • Not all atoms of the same element have identical mass. • These are called isotopes.

• Atoms are not indivisible. • Atoms are composed of subatomic particles.

The Atom

•Consists of subatomic particles • Electron • Proton • Neutrons

•Protons and Neutrons exist in the middle of the atom inside the nucleus • Protons have a positive charge • Neutrons have no charge – they are

neutral

•Electrons exist on different orbitals surrounding the nucleus • Electrons have a negative charge

Electrons, Protons and Neutrons • Atoms are composed of three smaller,

subatomic particles: electrons, protons and neutrons.

• Protons and neutrons are located in the nucleus.

• Electrons are dispersed throughout the remainder of the atom (mainly open space).

• Neutral atoms contain the same number of protons and neutrons to maintain charge balance.

The Effect of Subatomic Particles •Atoms can become ions by gaining or losing electrons from this sphere •Electrons are lost from atoms to form cations. •Electrons are gained from atoms to give anions

Atoms, Ions, Mass Number, Atomic Number •The number of protons and electrons are equal in an atom

•In an ion, the number of protons does not equal the number of electrons, providing a charge

•If the number of protons is greater than the number of electrons, the ion is positively charged and called a cation

•If the number of electrons is greater than the number of protons, the ion is negatively charged and called an anion

•The mass number is the number of protons and neutrons in the nucleus. This also determines the atomic weight

•The atomic number is the number of protons in the nucleus.

Atomic Number and Isotopes

•The atomic number is the number of protons in the nucleus of an atom •The atomic number determines the identity of the atom •Atomic numbers for every element are above the element’s symbol in the periodic table •Though all atoms of the same element have the same number of protons, atoms of the same element may have different numbers of neutrons

Isotopes of the Elements

•An isotope is an atom of an element which has the same atomic number, but a different number of neutrons from the element •The mass number is the total number of protons and neutrons for an element

Atomic Mass • Because the mass of a single atom is so small, it is inconvenient to use this as a mass unit. • Instead, relative atomic mass units (amu) are used. • Using carbon-12, C, as a standard, 1 atomic mass unit is equal to 1/12th the mass of a carbon-

12 atom.

• Since most elements are a mixture of isotopes, the atomic mass for an element is the weighted average of all naturally occurring isotopes of the element.

• To calculate the atomic mass: • Take the sum of the atomic mass of each isotope multiplied by its % abundance.

1 amu = 1.6606 x 10-24 g

Reading Review

What are the three subatomic particles?

What is the relative charge for the three subatomic particles?

What is the atomic number of an element?

What is an isotope?

What is atomic mass?