Atoms and Elements PDF

1️⃣ Chapter 2: Atoms and Elements Notebook 🧪 Principles of Chemistry Element- a substance that cannot be chemically broken down into simpler substances basic building blocks of matter composed of sin...

1️⃣ Chapter 2: Atoms and Elements Notebook 🧪 Principles of Chemistry Element- a substance that cannot be chemically broken down into simpler substances basic building blocks of matter composed of single type of atom, like helium Compound- a substance composed of two or more elements in fixed definite proportions most elements are chemically reactive and combine with other elements to form compounds such as water or sugar Subatomic Particles All atoms are composed of the same subatomic particles: Chapter 2: Atoms and Elements 1  Protons Neutrons Electrons The number of protons defines the element. All atoms of a given element have the same number of protons; however, they do not necessarily have the same number of neutrons Isotopes- atoms with the same number of protons but a different number of neutrons Chapter 2: Atoms and Elements 2  Two common notations for isotopes: X is the chemical symbol, A is the mass number, and Z is the atomic number. OR The chemical symbol (or chemical name) followed by a dash and the mass number of the isotope. Chapter 2: Atoms and Elements 3  Atomic Mass Natural abundances- percentage of the relative amount of each different isotope in a naturally occurring sample of a given element The atomic mass of each element is directly beneath the element’s symbol in the periodic table Ions The number of electrons in a neutral atom is equal to the number of protons in its nucleus (designated by its atomic number Z) In chemical changes, however, atoms can lose or gain electrons and become charged particles called ions Positively charged ions are called cations Metal elements, such as Na+, form cations Negatively charged ions are called anions Nonmetal elements, such as F–, form anions Avogadro’s Number A mole (mol) of anything contains 6.02214 × 10^23 pieces Chapter 2: Atoms and Elements 4  the value of the mole is equal to the number of atoms in exactly 12 grams of pure C-12. Molar Mass For atoms, you use the conversion factor: 1 mol atoms = 6.022 × 10^23 atoms To count atoms by weighing them, you need another conversion factor: The mass of 1 mol of atoms of an element is the molar mass An element’s molar mass in grams per mole is numerically equal to the element’s atomic mass in atomic mass units (amu) From mass to number of atoms From number of atoms to mass Chapter 2: Atoms and Elements 5 Chapter 2: Atoms and Elements 6