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AP Chem



Unit 1

1.0 Unit 1 Overview: Atomic Structure and Properties

5 min readjune 27, 2021


Dalia Savy


Jeremy Kiggundu

AP Chemistry 🧪

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Welcome to Chemistry! If you're like me, you're probably thinking about your life decisions, but do not fret! This study guide is here to help you navigate the triumphs and defeats, the epic highs and lows of AP Chemistry. Unit 1 will cover chemistry basics, including terms like a mole, Avogadro's number, atomic structures, and so much more. In this unit, you'll learn about how matter is formed and how chemists use specific units to measure amounts of matter, along with calculations involving unit conversions in stoichiometry. This unit develops the foundation for the rest of your chemistry career, so even though we describe it as "the basics," that doesn't make it any less important. In fact, all of these topics appear nearly every day in chemistry. Let's jump right in!

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Without a doubt, Chemistry is the most applicable science there is, which therefore makes AP Chemistry the most lucrative science class you could take while in high school! 
*Ahem* Don’t tell AP Bio kids that I said that🤫.
The content tested on the AP Chemistry Exam in May is about 7-9% of unit 1.

Key Vocabulary

molesmolar massperiodic tableavogadro's number
dimensional analysisatomsstoichiometrymass spectroscopy
isotopesaverage atomic masssolidliquid
gasformula unitslaw of definite proportionsempirical formula
chromatographypolarityelectron configurationsdalton's theory
coulomb's lawthe bohr modelthe aufbau principlethe pauli exclusion principle
hund's rulenoble gas shortcutvalence electronscore electrons
photoelectric effectionization energyatomic radiusnuclear charge
electron electron repulsionionic radiuselectronegativityelectron affinity
metalnonmetalmetalloidionic bonds
polar covalent bondsnonpolar covalent bondscationanion

Intro to Chemistry

Unit 1 is titled "Atomic Structure and Properties." As such, the unit surrounds one central object: the atom. An atom is the smallest subdivision of an element that maintains the properties of that element. The atom is the primary object in chemistry. It makes up everything around you. Atoms make up molecules and compounds that can react with each other to form other compounds. You'll learn what makes up an atom and a little bit of quantum mechanics to understand where exactly these things are. The main parts of an atom are the proton, the neutron, and the electron, the most complicated being electrons. Different models of the atom have shown these three things differently, but today, chemists use quantum mechanics to define orbitals which you'll learn more about moving forward.
Chemists measure the number of atoms in a mass of a substance by using the mole. Moles are similar to a dozen in that it describes a discrete number of something. A mole of something is equal to 6.022 * 10^23 of that thing. A mole of any given element or compound is 6.022 * 10^23 atoms/molecules. This number is known as Avogadro's number and is formally defined as the number of Carbon atoms in 12 grams of Carbon-12. The conversion factor from moles to grams and vice versa is known as molar mass and is seen in the units g/mol (or the reciprocal mol/g). Unit 1 focuses intimately on dimensional analysis, commonly known as "unit conversions." Most chemistry problems focus on converting between units, so practicing this skill early on is super important.

Major Topics Covered

There are two major "groups" in unit 1, those involving mass and matter and those involving atomic structure.

1.1-1.4: Mass and Matter

In the universe, anything that takes up space and has mass is matter. As we discussed before, all matter is built from atoms. Unit 1 will cover some major types of matter, such as molecules, compounds, elements, and pure substances, which all have distinct definitions and compare to each other in different ways. Understanding the different types of matter will help you better understand how matter works in the world. You'll also be introduced to the basic states of matter: solids, liquids, and gases, though you've probably learned this in earlier classes.
When chemists discuss matter, they do so in terms of moles. Moles help describe the amount of matter (note that this is different from mass, but there is a connection). Molar mass serves as a conversion unit from moles to grams or vice versa. For example, the molar mass of Carbon is 12.01g/mol Carbon.
When calculating molar mass for an element, chemists use mass spectroscopy, which is a process that measures different isotopes for their relative abundance, and then uses a weighted average to find the average atomic mass, which is also the molar mass.

1.5-1.8: Atomic Structure

When discussing atoms, we also spend time discussing what an atom actually is. There are three main parts to an atom: protons, a positively charged particle, neutrons, zero/neutral charge, and negatively charged electrons. The protons and neutrons make up the nucleus, whereas electrons orbit around the nucleus. The primary question of quantum mechanics in this unit is "where are the electrons"? You'll learn about electron orbitals which attempt to define zones where electrons probably are. For specific atoms, electrons have certain configurations dependent on quantum numbers that determine their orbital and position.
You can see electron configurations using PES, photoelectron spectroscopy, which shows an abundance of electrons at certain energy levels. The CollegeBoard loves to test whether or not you can read a PES spectrum, so make sure to pay attention to this! 
The atomic structure can also help us define trends across the periodic table. You'll cover the trends for electronegativity, electron affinity, ionization energy, and atomic/ionic radius. These can be justified by thinking about effective nuclear charge, which is the force experienced by an electron in an orbital.
Electrons also come into play in ionic compounds, which involve a transfer of electrons to form a positive and negative ion held together by Coulombic attraction.

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⚛️Unit 1: Atomic Structure and Properties
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