Chem10 Ch.4: Atoms and Elements

Atoms

invented by the Greeks, as the only way to explain change, rearrangement of uinchanging pieces with space between them

Dalton's Atomic Theory

All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed.

J. J. Thomson

postulated the existence of negatively charged particles, called electrons through mysterious rays he observed bending towards a magnetic field that light doesn't do. he determined the charge-to-mass ratio of an electron. he reasoned if an atom is negatively charged it must also be positively charged because atoms are neutral.

Plum Pudding Model

By J. J. Thomson,

Pros: only contains what he knows scientifically, assumed simple distribution that he knew nothing about

Cons: Had Little chance of being right and violated basic physics because negative charges touching positive charges would be negative infinity (so its wrong)

Robert Millikan (1909)

Performed experiments involving charged oil drops

Determined the magnitude of the charge on a single electron

Calculated the mass of the electron

Henri Becquerel (1896)

Discovered radioactivity- spontaneous emission of radiation from the nucleus. He found the three kinds of radiation: negatively, positively and neutrally charged.

Ernest Rutherford (1911)

classified three types of radioactive emission based on their penetrating power instead of charge, showed the plum pudding experiment to be wrong, and found that the atom has a dense center around the nucleus

Alpha (α) radioactive emission

a particle with a +2 charge (least penetrating), heavier than other types of radiation

Beta (β) radioactive emission

a high speed electron (-1 charge)

Gamma (Y) radioactive emission

high energy light (neutral) (most penetrating)

Rutherford's Gold Foil Experiment

proposed that atoms consist of a tiny, massive, positive nucleus surrounded by electrons, and matches the nuclear model

Nuclear model

Mass is concentrated at the center, very light electrons fill the volume, mostly no deflection, ocassionally big deflection, and matches the gold-foil experiment

Atom contents

Electrons(-): outside the nucleus, much lighter than protons and neutrons, spread out

Protons(+): in the nucleus, positive charge is equl to negative charge, tiny, but dense

Neutrons: in the nucleus, no charge, density similar to proton, but slightly heavier

Neutron

hypothesized by Rutherford in 1920, discovered in 1932 by James Chadwick, no charge, density similar to proton, but slightly heavier

Atom Nucleus

Center protons and neutrons

Electrical charge

positive and negative electrical charges attract each other and same charges repel each other, they cancel each other out.

How atoms of the elements differ from one another

elements are defined by the number of protons in the nucleus, if an atom had a different number of protons, it would be a different element

alkali metals

Lithium, Sodium, Potassium, Rubidium, Cesium, Francium (reactive, explosively reactive with water)

Alkaline Earth Metals

Beryllium, magnesium, calcium, strontium, barium

(Less reactive)

Halogens

have different physical properties but have similar chemistries; fluoride, chloride, bromine, iodine.

Noble Gases

helium, neon, argon, krypton and xenon

(they are not reactive, but Kr and Xe form a few compounds)

The Periodic Table

(broadly classified as metals, nonmetals and metalloids) developed in 1869 by several scientists, Mendeleyev's version became famous because he used his table to predict the existence of yet unknown elements and their properties. Most elements are metals and nonmetals are huddled towards the topright corner

Periods of The Periodic Table

A horizontal row of elements in the periodic table. There are 7 periods

Families of the Periodic

(groups) elements in the vertical columns, having similar chemical properties. There are 18 groups

Properties of Metals

occupy left side of periodic table, good conductors of heat and electricity, malleable, ductile, lustrous, tend to lose electrons as they undergo chemical changes

(Ex: iron, magnesium, chromium and sodium)

Properties of Nonmetals

occupy the upper right of periodic table, the dividing line is the zigzag line from boron to astatine. Nonmetals have varied properties some solids, while others gases, as a whole are poor conductors of heat and electricity.

(Ex: oxygen, nitrogen, chloride and iodine)

Properties of Metalloids

metalloids lie along the zigzag line splitting metals and nonmetals. Semiconductors, making them useful in electronic devices

(Ex: Silicon, Arsenic, and germanium)

atoms lose or gain electrons to form..

ions,The charge of an ion is on the upper right cornel of a symbol. these elements don't always exist as ions.

(Ex: Mg^2+)

cation charge

main-group #

(1A, 1B, aluminum)

positive ions are called cations

Anion Charge

(main-group #)-8

(5A-8A)

negative ions are called anions.

Ion Charge Formula

= (#p^+) - (#e^-)

Isotopes

Atoms of the same element that have different numbers of neutrons, all atoms must have same amount of protons; in nature most elements are mixtures of isotopes.

Atomic Number

the number of protons in the nucleus of an atom

(z=p)

Atomic Mass Number

the total number of protons and neutrons in an atom's nucleus

(protons + neutrons)

isotope name

Element-mass number

(Ex: 24 over Mg is magnesium-24)

Atomic Mass Unit

meant to approximate the atomic mass number, in general can't be exactly equal. When used by itself means the weighed average (can't be whole) of the isotopic masses of its isotopes in a.m.u.

Mass Spectrum

graph that gives the relative mass and relative abundance of each particle.