Number the elements sodium , magnesium, and potassium in the predicted order of ionic radius from the largest 1 to the smallest 3

1 potassium

2 sodium  

3 Magnesium

The ionic radius is the measure of an atom's ion in a crystal lattice. It is half the distance between two ions that are barely touching each other.  

The ionic radius may be larger or smaller than the atomic radius (radius of a neutral atom of an element), depending on the electric charge of the ion. Cations are typically smaller than neutral atoms because an electron is removed and the remaining electrons are more tightly drawn in toward the nucleus. An anion has an additional electron, which increases the size of the electron cloud and may make the ionic radius larger than the atomic radius.

•As you move from top to bottom down an element group (column) ionic radius increases. This is because a new electron shell is added as you move down the periodic table. This increases the overall size of the atom.

•As you move from left to right across an element period (row) the ionic radius decreases. Even though the size of the atomic nucleus increases with larger atomic numbers moving across a period, the ionic and atomic radius decreases. This is because the effective positive force of the nucleus also increases, drawing in the electrons more tightly. The trend is particularly obvious with the metals, which form cations. These atoms lose their outermost electron, sometimes resulting in the loss of an entire electron shell. The ionic radius of transition metals in a period does not, however, change very much from one atom to the next near the beginning of a series.

Values for ionic radius are difficult to obtain and tend to depend on the method used to measure the size of the ion. A typical value for an ionic radius would be from 30 pm (0.3 Å) to 200 pm (2 Å). Ionic radius may be measured by using x-ray crystallography or similar techniques.

Potassium 1.38 Å

Sodium 1.02 Å

Magnesium 0.72 Å

pre-sliced bread is a relatively recent development in baking technology. previous to that, it was always sold in a bakery in daily-made contiguous loaves with no wrapping, and was moderately perishable, usually being used with a day or two (which is why every bakery had a discounted “day-old” bread table.) therefore, pre-sliced bread would grow stale quickly. the hard crust provided a protective layer, and once the exposed dry slice left from the previous cut was removed, the interior was still soft.

what keeps bread soft is the moisture retained in the crumb (the light spongy part that’s not crust). the reason the crust develops is the surface of the dough gets exposed to hot dry air during baking which browns the outer layer and seals it, preventing all the moisture from escaping the dough. longer exposure to air will also eventually cause your bread to lose flavor and become stale.

people were used to cutting slices as they needed them and storing bread in a specially-made wooden or metal breadbox or pail with a lid to preserve it longer, but the first automatically sliced commercial loaves were produced on july 6, 1928, in chillicothe, missouri, using a machine invented by otto rohwedder, an iowa-born, missouri-based jeweler.[1] pre-sliced bread would indeed dry out, were it not for another 20th century technology: the plastic bag. bread could now be pre-sliced, and if the enclosing bag remains sealed as much as possible, the bread will remain soft and fresh for longer than if sitting unwrapped on a shelf or enclosed in a bread box that is not air-tight. sealed packaging meant bread could also be sold on store shelves and eliminate frequent trips to a bakery.

sealing bread in a plastic bag had another effect: the moisture in the loaf will re-distribute into the crust and soften it, which is sometimes more pleasing in a sandwich - especially for children whose teeth might not yet be strong enough to tear through a hard crust. a homemade loaf of bread can be sealed in a bag overnight and the crust will become soft like store-bought sandwich bread.

these were novel changes in how bread was produced and sold, which led to the coining of the phrase “the greatest thing since sliced bread.”