AP Cheistry Unit 1: Atomic Structures and Properties (7-9%)

1.1; Moles and Molar Mass, 1.2; Mass Spectra of Elements, 1.4; Composition of Mixtures - Mathematical Routines | 1.3; Elemental Compositon of Pure Substances - Question and Method | 1.5; Atomic Structure and Electron Configuration - Models and Representations | 1.6; Phtoelectron Spectroscopy, 1.7; Periodic Trends, 1.8; Valence Electrons and Ionic Compounds - Model Analysis

Why do chemists use moles?

a) Particles can not be directly counted

b) They use moles to connect the mass substances reacting and the number of particles undergoing chemical changes

What is Avogadro’s number (same number of particles for each sample)?

6.022 × 10²³

Why is 6.022 × 10²³ essential to know?

Its the number of things in a mole. Even though the samples contain the same number of particles, their mass is different.

Why are their mass different and the number of particles the same?

Because the constituent particles in each sample are different.

How to find the mass of one molecule or particle?

1. Count the atoms in the chemical formula

2. Find the atomic mass of each element on the periodic table

3. Multiply atoms by atomic mass to find mass per element

4. Sum the results to find the total formula mass

Why do chemists use molar mass? And how?

Molar mass is used to convert quantities between mass units (grams) and count units (moles)

What is the mathematical relationship between moles and molar mass?

1 mole = molar mass (g)

What is a conversion factor?

A ratio (or fraction) which represents the relationship between the same quantity in two different units (used to convert from one unit to another)

How do you use the conversion factors?

When converting a known quantity from one unit to another, multiply by a conversion factor with the starting units in the denominator

What is a mass spectra?

A technique used to identify the isotopes of an element and their relative abundance in nature

How to estimate the average atomic mass from a mass spectrum?

1. Identify its isotope’s masses and percent abundances from the graph

2. Multiply each isotopes’s mass by its relative abundance (not percent abundance)

3. Add the results

How to determine the mass spectrum from a graph?

1. Identify isotope’s masses and approximate abundances from the graph

2. Estimate the average atomic mass

3. Compare your estimate to atomic masses on the periodic table

Can two different substances have the same percent composition by mass?

Yes

What is the empirical formula?

The lowest whole number ratio of atoms of them elements in a compound

How do chemists use them?

To determine them through the mass data generated from laboratory analysis

How to convert the mass of elements or its % composition to the empirical formula?

1. Convert masses to moles

2. Divide by lowest number of moles

3. Use mole ratio to write the chemical formula

Define elemental analysis

Finding the relative mass of one or more elements in the mixture (how pure a substance is)

What are the structures of an atom?

Atoms have a positively charged nucleus (protons and neutrons) surrounded by negatively charged electrons

Define Coulomb’s Law

Used to calculate the force between two charged particles (either pushing or pulling)

What is Coulomb’s Law formula?

F α (q₁q₂)/r²

How does the ionization energy involve with Coulomb’s law?

Coulomb’s law can be used to predict the amount of energy required to remove an electron from an atom

How do you know which electron is the easiest to remove? The one near the nucleus or the one furthest?

The electron further from the nucleus because the force of attraction or the distance is weaker compared to the electron that is closer to the nucleus

What does “Aufbau” Principle discuss about?

Aufbau = to build up; and states that electrons fill lower energy levels first and then fill the higher ones

How do we know this fills higher in that order?

Photoelectron Spectroscopy

What is photoelectron spectroscopy?

Experimental technique to determine the relative energies of electrons in atoms or ions

What are the name of the electrons that are located in different energy shells/subshells?

Valence electrons - the easiest to remove and the greater the distance to the nucleus

Core electrons - the hardest to remove and the lesser the distance to the nucleus