Arranging the Elements

Dmitri Mendeleev

A Russian chemist, discovered a pattern to the elements in 1869. First he wrote the names and properties of the elements on cards. Then, he arranged his cards by different properties, such as density, appearance, and melting point. After much thought, he arranged the elements in order of increasing atomic mass. When he did so, a pattern appeared.

Metals

A metal is a material (an element, compound, or alloy) that is typically hard, shiny, and has good electrical and thermal conductivity. Metals are generally malleable — that is, they can be hammered or pressed permanently out of shape without breaking or cracking — as well as fusible (able to be fused or melted) and ductile.

Group

A vertical column of elements in a periodic table; elements in a group share chemical properties. Elements in the same group have similar chemical and physically properties. For this reason, a group is called a family.

Periodic

Describes something that occurs or repeats at regular intervals. Example- The days of the week are periodic. They repeat in the same order every 7 days. Mendeleev found the elements' properties followed a pattern that repeated every seven elements.

Period

In chemistry, a horizontal row of elements in the periodic table. The physical and chemical properties of elements in a row follow a repeating, or periodic, pattern as you move across the period. Properties such as conductivity and reactivity change gradually from left to right in each period.

Prediction of Germanium

Mendeleev predicted the Atomic mass(70), Density(5.5 g/cm-square), Appearance(dark grey metal), and Melting Point(High melting point). All of the predictions Mendeleev made were so close to the original product.

Periodic Law

The law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements.

Metalloids

The metalloids; boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), polonium (Po) and astatine (At) are the elements found along the step like line between metals and non-metals of the periodic table. Metalloids have properties of both metals and non-metals. Some of the metalloids, such as silicon and germanium, are useful in semi-conductors. This property makes metalloids useful in electronic components.

Nonmetals

The non-metals or non-metallic elements; hydrogen (H), carbon (C), nitrogen (N), oxygen (O), phosphorus (P), sulphur (sulfer) (S), selenium (Se), and the noble gases form a relatively small group with a step like pattern towards the left-hand side of the periodic table (hydrogen being the odd one out on the right of the table). Non-metals are not strictly defined, but tend to show characteristic properties like poor heat and electrical conductivity, form acidic oxides, dull low lustre and brittle, low densities, low melting points and high electro negativity.

Predicting Properties of Missing Elements

The picture beside shows part of Mendeleev's first try at arranging the elements. The question marks show gaps in the pattern. Mendeleev predicted that elements yet to be found would fill these gaps.